I have done some work to fix U++ appearance with linux 'dark themes', especially Dark Room (which has a nasty feature where view background is white, but dialog background is dark).
I guess it works quite fine now w.r.t. to colors.
Anyway, then I have noticed that menubar and toolbar icons, designed for "normal" (light background) themes, do not look all that well in dark themes. So I have tried to implement "inversion" algorithm that automatically adjusts icons to look better on dark background (it is a new AdjustForDarkBk function in Draw).
I would welcome if somebody could check whether this is any improvement