SkyLight color

Dunno if that is the right forum but here it is.

My goal is to add, more configurable SkyLight coloring. Now we have two options. Color of upper hemisphere, and color of down hemisphere. The issue is that down one, can be either black or the same color as upper. Which is honestly not enough.

I actually found where in C++ colors are set, but at this point I hit wall, because I can’t find what is going on with this parameter. I guess it is passed to shader.

The question is to which one ? If someone could point me to the right shader file it would be very nice.