osu! won't subtract the colors or separate color channels. They are mostly blended mulitplicatively with the images. For example if you colour selection-tab.png cyan, it will appear purple ingame, not red.
I just added that column. Along with that I moved most of the remarks and notes about colours into that column as notes.
Feel free to correct me if I use the wrong terminology.
On a side note: lighting.png is still used in osu!taiko during kiai time and can be used on beatmap skins. When I was experimenting with it I added a black background to my sliderfollowcircle and used it as lighting. During osu!taiko it was really prominent due to its size. I never noticed it since lighting is hidden behind the bar images on the hit position. I also blanked out the taiko-bar-right images. This may be a layer order mistake when the new taiko skin was included.
EDIT: clarified how I found lighting for taiko.
I just added that column. Along with that I moved most of the remarks and notes about colours into that column as notes.
Feel free to correct me if I use the wrong terminology.
On a side note: lighting.png is still used in osu!taiko during kiai time and can be used on beatmap skins. When I was experimenting with it I added a black background to my sliderfollowcircle and used it as lighting. During osu!taiko it was really prominent due to its size. I never noticed it since lighting is hidden behind the bar images on the hit position. I also blanked out the taiko-bar-right images. This may be a layer order mistake when the new taiko skin was included.
EDIT: clarified how I found lighting for taiko.