I’d like to emit a very specific dark, but non-black color, so that the emitter casts this exact color onto other objects.
When I select this color and up the strength in cycles, it turns white instead. How to I make the rays not “brighter”, but rather increase the strength of that dark color?
Thanks for sharing, I’ll play around and see if I can get this to work.
What about preserving the shading that the sphere recieves though too, and the lighting effects? Like if you have a flowing lightbox in real life, you can still cast light and shadows onto it from other light sources and objects you place on top.
Sorry but I tried your method and it didn’t work. Increasing the strength still made the color turn white, rather than increasing its radius of effect.
Actually, it’s a funny thing: you can set color values in an emission shader to negative values:
Just keep in mind that nothing including shaders, color management and other features are designed with this in mind, so this can break a lot of things and you are not really supposed to do this, but still this could be used to atchieve some non-photo-realistic effects if you keep in mind it is as is.
It used to be possible to enter negative numbers in RGB input directly in old versions, but it’s not any more for quite some time(many versions now), but it still works if you just plug something that has negative values to the color input.
This is not something that is ever done in any normal workflows though. It’s not something that you need for every-day kind of stuff, so please consider if whatever you are doing should be done some other way first. 
Actually, really, nothing is supposed to be done this way. You should not do this But it works… 
You could try something like this:
The light path node lets you decide separately the strength of the emission object and the light it casts.
The Light falloff set to constant helps spread the light at low values, even so the higher (brighter) the light strength, the brighter it will be but at least you can control how bright the emission object is and how bright the light is (or how dark)
Here the sphere is casting the light.
Ps for this I had to clamp the direct light a bit to get rod of some dark “fireflies”
So, you want a weak light that influences a long distance? Would this be satisfying?
This is done using the light falloff node. It’s a light that doesn’t weaken with distance. I also used the light path node so the look of the emitter can be tweaked separately from the light it emits.
Here is the file.
dark_light.blend (1.2 MB)
