ypoissant, while the gamma may be correct in you version, i can’t agree that the colors are.
what you have done is reddened the sunlight, without changing the color balance enough.
the result is vibrant blue shadows.
in reality, the shadows would be much darker, and less blue.
the reason, as follows;
in the middle of the day, the sun is overhead, thus the sunlight passes through the least atmoshere possible.
the overall color is pure white, by definition.
however, the light coming from the direction of the sun is slightly yellow, because the blue light scatters a lot, which gives you more blueish “fill” light–the light coming from all directions.
near sunset, the sunlight passes through more atmoshere, more blue light is scattered, thus the obvious yellow-orange-red effect.
however, the blueness of the shadows does not increase proportionally.
also, there is less light overall, because the sun is at an angle.
spacetug, I invite you to pick one of the rendered image and tweak them in Photoshop or any other application and show us how you would improve the lighting. The scattering-in-atmosphere theory is correct and interesting but I tried to show by example and not just lecture on light scattering.
Thanks again for the comments!
I have not yet finished working, so I will post the image tomorrow.
Just to some of the comments:
@ OrchidFace: Thats probably right 
I am working on the textures right now. But I will have to restrict the amount of detail I add, to keep the workload on a reasonable level. As written in my first post, the scene is “only” the background for some fantasy characters. But those are waaay behind when it comes to reality. So improving the characters has priority over the scene now, otherwise they will look like comic figures glued to a photograph
But maybe I will do something more interesting with the scene afterwards. I begin to love the scene.
@ Azmisov: same thing. Really nice idea, but probably exceeding my skill level right now. I might actually do the scene again alone and with some more interesting details. But not yet
@ ypoissant: That is way too red for my taste. I want to have a late-afternoon scene, where the sun is low, but not yet really red. So, no sunset. I will make the light a bit softer maybe, but I will try both your and spacetug’s suggestion.
@spacetug: thanks for the ivy-gererator. Thats amazing!
ypoissant–thank you, i just might accept your “invitation”, or should i say challenge?
kundera, you’re welcome
what kind of fantasy? 
edit:
to avoid double post, i’ll just use this one
this is what i would consider to be 1-2 hours before sunset :yes:
oh, and ypoissant, i’m sorry, i didn’t mean to lecture.
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If you are not looking for true “just before sunset” but rather late afternoon, then I would push the yellow-blue contrast as attached and I would go even brighter than that. You will probably not want to push that far but this example gives you a good range of options.
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i would like to present an example:
we all know that Cars was a successful movie
in this image, there is a mid- to late-afternoon feel
the foreground has a warm feel, somewhat yellow
but, the shadows are black
not blue
however, in the background, the mountains, the shadows are very blue
there is a reason for this.
it’s the same reason as why the sky is blue;
there are several miles of atmosphere in the way
i would contend that ypoissant’s latest image has the white, washed out feel of noon, with twilight colored shadows added
i realize that it was exaggerated, but way too much
So, I am back with an (hopefully) improved image. I did work a lot on the textures. They are not perfect and i will need to add some bumps here and there. I also forgot about the stone-wall part in the lower left, but as render times are rising, I am too lazy to re-render today. Generally, this is now as “real” as I want it to be. So, you may of course keep on commenting, but i will not change major parts before I finished my characters.
I played around a bit with the light. The current setting is a very slight blueish taste on the shadows (hard to see, I admit) by making the AO a little blue. I think blueish shadows are basically a good idea (even in the foreground: one can also see it there in the cars-image). I also adapted the color of the sun, to make it more afternoon like. I might redo the lightning when I put in the characters.
@ spacetug: I am playing pen&paper role games, and I decided to model my group, which means five characters (4 human and one dwarf). I still have to work a lot on the characters, but I am hoping to finish the whole thing within the next three weeks. Let’s see.
So, thanks for your help so far. Keep on commenting, if you like. Its amazing how far I was able to push my own limits with the help of your advices. 
OK, let’s talk atmosphere scattering then.
The atmosphere appears blue because it scatters the blue part of the sun’s spectrum. Because a lot of the blue part of the sun’s spectrum is scattered in the atmosphere, the direct light coming from the sun looses of its blue component and becomes yellow as a consequence. A scene lit by a clear sunny sky receives two different lights: 1) the direct sun light which is yellow and very directional and 2) the ambient sky light which is blue and very diffuse. In other words, what is not directly lit by the sun is lit by the blue sky. So because of this, shadows appear blue.
As the atmosphere thickens, it scatters more of the sun light and starts scattering some green. This is the case as the sun approaches sun set or sunrise angles. The consequence of that is that the sun light, loosing not only its blue but also its green becomes orange. And the shadows shift toward the greens.
That is the theory that explains why the sky is blue and the sun is yellow. The yellow-blue contrast have been in used for centuries by artist painters. Maxfield Parrish comes to mind. This observation can be used moderately or abused for effects (personally, I like to abuse it). This yellow-blue contrast is also visible in photos or real outdoor scenes. The yellow-blue contrast is also used in a lot of movies.
A very good source of documentation on lighting in general is from Itchy Animation. This is a must read for anybody interested in lighting.
The use of yellow-blue contrast induces a tension because of the implied warm-cold contrast. This can be used for artistic effects. For some reasons, blue shadows don’t need to be very dark to convey the feeling of shadow. Actually, the shadow part of a picture could have very nearly the same values as the sunny part and still convey unmistakably light-shadow feeling. Because of that, it is possible to very clearly see details in shadow areas. Blue shadows gives the artist more latitude for showing details.
The fact that far away mountains take on a blue tint is also because of the blue light scattering in the atmosphere. As the object is farther away, then more of that blue light is scattered back in out eyes and adds to the lights that is received from the object. This is called atmospheric perspective.
After all that is said, it is still no argument for or against the balance between yellow and blue in a render. It is, in the end, just a matter of taste.
BTW, I took the color picker in Photoshop to sample the shadow areas in the foreground of the poster you posted and all the samples I took were in the blue zone of the Hue with very low Lightness which may look like black on your monitor but those shadows are definitely blue.
Pretty strange, I can only see the picture in my last post when I am logged in. So, maybe you do not see it as well?
Does anyone know, why this is the case? It’s a thumbnail from ImageShack.
Well, just in case, here is the image again, but in lower resolution:
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The texture addition look good and add nice details in the surfaces. Lightingwise, it is to dark for a sunny light feel, even if late afternoon. It feels like the sun was behind an eclipse or the camera was set with a too low aperture.
ypoissant, i realize the shadows are slightly blue, but they are no vibrant blue like your Photoshopped version
too much emphasis in cold, blue shadows draws from the warm, late-afternoon feel
since this image is, in the end, meant to be a background, it shouldn’t draw too much attention.
it should merely set the overall mood
kundera-
imageshack is working just fine for me, thought they do seem to have pop-ups, which is annoying
about the image, i think the overall lighting is okay, but you should do some post-processing with the composite nodes to fine-tune the brightness and color balance
about the textures, i don’t like the repetitive effect of the one on the near building on the right
and i think the rocks were better before
i like the new ivy, it’s much better
and the sacks look good now
i would say that if you fix the right-hand building, put the rocks back to the previous texture, and give the stone wall a proper texture, and did some brightness/color correction, you could call it done
looks good ,how about light with little halo coming out of the window ,and add some carts and tree ,barrels .etc…makes it look realistic .and the ground could use a little bit of bumpiness .and other then that …it really looks great
Thanks for your suggestions again. I will see, what I can do
At the moment, I am still wondering about the right light setting. I had a train journey of about two hours this evening, which gave me plenty of time to watch the light and shadows. Its right, the shadows are blueish and not very dark and the light has a distinct yellow-orange color.
My problem now is: How do I accomplish that in blender? I tried a bit with making the AO more blue and brighter, but then I have to turn the sun almost entirely orange to compensate for the blue AO in the bright areas. I did not like the effect.
On the other hand, I tried to set AO to sub and add a blueish hemi-lamp instead. But then, there is a similiar effect. Additionally I then have some totally black shadows beneath the roofs. :no:
Considering the reason for the blue-shadow-effect (i.e. the diffuse blue light all around) these methods should work.
So, question to you: Have you tried that before? Do I just have the wrong color/brightness-settings or am I missing something?
Would be glad about your help, because re-rednering the (even simplified) scene a dozen time is no fun.
Make the AO blue color subtle and turn the shadow color on your hemi or sun to an almost black shade of blue. Make the color of the sun a little yellow-orange. Don’t make the discoloration of light or shadows very far from white or black.
Oh, and a little bit softer shadows from your last render would do well.
I know the issue you are reporting very well, that is how to compensate for the blue light casted all around to get a yellow sun. This problem comes from the fact that our eyes adapt very well to the high contrast between shadows and sunlit areas and we perceive the sahdows areas much brighter than they are in reality. So to get the same effect, we would need to set the sun intensity very high and this would burn out all the sunlit areas. You could use a tone mapping algorithm to compensate for that but that adds yet another layer of complexity and control difficulty.
A simple solution I used in the past in another 3D software, was to place two sun lights at the sun position. The yellow sun and a blue negative sun that I used to cancel the blue cast from the AO. This way, it was much easier to control the contrast between the blue and the yellow and not polute the yellow with the AO blue. I would think that the same technique would work in Blender too.
My only Beef, is that this looks nothing like medieval anywhere… maybe some former roman villages but not medieval Europe by any stretch of history. The Dark ages and Medieval Europe were far poorer than the ability to build multiple plaster structures, Wood, straw and mud where how people lived back then, not your Medieval Utopia… this might be classified as early Renaissance. Ok, enough of my ranting… I really like the render, it is very put together with lots of nice details.
- You seriosly need to change the uniformness of the orange roof on left.
- Work on the outer shapes of the shutters, they need to be more detailed.
- Some tweaking of the lower left little stone wall would be good. It has very hard edge which looks very unreal once it catches the eye.
- Put ivy on the right wall close to the camera to hide the tiling.
- “Randomize” the edge of the wall on the left.
- And work on the planks on the house that’s at the end of the street. This wouldn’t be sufficient, check these: http://images.google.cz/images?hl=cs&lr=&um=1&sa=1&q=medieval+house&btnG=Vyhledat+obrázky&aq=f&oq=
- I would also fix the materials close to the right wall, so they aren’t wholly black. (at least something should be seen)
Sycosys: I am sure there were at least “some” villages where people weren’t so poor because they had vast lands lands and a good lord :-).
Here is a link to some medieval wall textures I’ve created based on historical sources.