Hi there.
I’ve iluminated an exterior scene with Sky Texture, model Nishita, but it dyes everything in a yellowish tone.
I tried to change the ozone and air values, but I can’t make light more neutral, unless I raise the sun, which is not an option for my scene.
I tried the Hosek/Wilkie model and I really like it, except it always seems cloudy, so very little direct sunlight appears projecting on the surfaces.
Can anyone guide me with this ?
For Nishikita Sky, by default, Strength of Background shader is set to 1.
That is too bright to see gradient of sky. Sky is not supposed to have same importance as Sun.
So, you have to set it to 0.1, first.
Then, you can set all settings to 0 to end-up with a black sky.
Then, you add a little bit of air.
Below 0.5, ground at the horizon will be white. Between 0.5 and 1, it is yellow. Between 1 and 2, it is a brownish orange. Above 2, it is red. At 4, it becomes violet. At 5, it becomes black. Above 5 the gradient moves up above the horizon.
Ozone will squeeze the gradient of colors and accentuate contrast before making everything darker.
Dust is, first, blurring bright spots (That is why a strength at 1 for the whole sky is a bad idea). Then, it is elevating the glow to zenith, to emphasize that dust is thicker on the ground.
For Hosek//Wilkie, you can not lower turbidity below 1.
No Sun is visible with that model. You only make its position noticeable by increasing glow around it, by increasing turbidity.
By increasing glow around the sun ; you are making horizon, at the opposite of sky, more contrasted, but more blurry, below the sun. That is a trade-off.
So, you need to use color nodes to increase contrast, if it is too cloudy for you.
For Preetham model, by decreasing turbidity below 1.2, ground albedo is increased.
Between 1.2 and 1.6, it corresponds to night skies. Above 1.7, you need to decrease Background strength. You don’t accentuate position of Sun. Everything just becomes more cloudy.
Sky textures are textures. You can mix several of them to obtain desired result.
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As zeauro, have said, I also set strength of the texture to 0.1 , leave sunlight intensity as it is though.
Turn off any other main light if you have it active, the nishita models own light intensity is what you need foremost, not any other additional light unless being a manmade light source or other phenomena.
Increasing the ozone from 0-5 and even above will help make the sky bluer, but not the illumination color on objects, for that you have to make sure air molecules are not too dense, that is the air values …maybe around 0.2, if you go above that the airmolucules will start to kick in as denser atmosphere…which means the blue wavelengths can´t penetrate it enough, and it starts to become yellowish, and more of it and it turns red.
The combination of high ozone and high air density will give you sort of pinkish purple color.
So all you got to do is set the air density very low, especially if the sun elevation is low, then it has to pass through such distance in the air that light in nature physicly change color, so you can think of it as no air, it´s like in space, just cold bright light, so cut of the air, especially if you are setting up a high altitude scenery in the alps 
Once the sun elevation goes beyond 0, sun color will not affect the objects front parts, unless you have an object high up in the sky… it will be obscured by the horizon.
So you should be able to get similar look to that of the hosek model.
hosek model is a bit faster though, but it lacks a proper sun connection to any distandt light for position, which you probably could set up right with some channel drivers, I think I did that once but forgetten how too…I usually use the nishita model for final scenery, hosek for fast test purposes, and with the hosek model, I never set it to preetham.