Hey guys, thanks! I worked with red, green, blue so far but for thunder strikes I want to color the skies entirely in white. Sadly, working with mtl_sky has absolutely no effect (Which is weired, mtl_terrain and mtl_model work as expected).

So I guess I'll have to add another sky layer to achieve lightning.

mtl_sky(.emissive_...) affects the color of the sky only when red,green,blue is lower than 255. And the opposite way, red,green,blue only make changes when mtl_sky.emissive_... is lower than 255.

So it seems the light formular is simply mtl_sky.emissive_...+[sky].red/green/blue, with the maximum of 255 for sure.

The only (fast) way I see to make the sky completly white is to use a shader. Making a another sky layer is very framerate unfriendly.

strange, I just tested, and I can set ambient and emissive for a sky cube by mat_sky, thus can achieve a totally white sky, without touching entity rgb.
only dome and cylinder are not affected by it.

I didn't try emissive yet and will do now. Thanks for testing.