Added ability to reduce illumination color saturation. It is a kinda fake white balance adaptation. Real white balance adaptation as a post-process will make all planets looks like Earth, with distorted colors of the star sky, This is not what I want from SpaceEngine. But reducing incoming sunlight saturation by just 30% makes very large difference! Compare these screenshots of TRAPPIST-1 d before and after:
TRAPPIST-1 star has a surface temperature of 2560K - just like a filament of a light bulb. So illumination on a planet must remind illumination under light bulb, perceived colors must not be so yellow as in SE before.
Maybe the Moon is a better example:
Next, added ability to choose the color system used to generate the Planck (thermal) spectra colors. It is kinda a white point/white balance settings, used to convert computed Planck spectrum into RGB values. There was a multiple systems available in all versions of SE, but no ability to switch between them. I choose the SMPTE system ages ago, but now you can choose the one you like better. This settings affects appearance of hot surfaces such as sun photosphere and lava, also affects color of sunlight illumination (but not so much as simple desaturation). Comparison of SMPTE and CIE systems are below.
I also made a small trick to reduce aliasing of a star surface textures (suppressing the granulation on the upper LOD levels). Screenshots shows TRAPPIST-1 before and after.