In D11262#237017, @Pitel wrote:

I guess I should have renamed it from isLightColor to something like isNotAlmostBlack... The point was to replace almost black colors with real black because it looks better with opacity. IMHO (0,0,128), which is deep blue, is far enough from black to not mess with it because font colors readable on deep blue background might not be readable on black one.

Ah okey. I had the impression this was used to decide if light or dark text needs to be used. I wouldn't want to see black text on dark blue buttons :)