Afaik Kawaks uses 16-bit color resolution and I haven't seen any option nor INI entry to modify that. You can adjust brightness on menu "Video" -> "Adjust Brightness" only for CPS2 games, but you might correct the color Gamma values for every game on "Video" -> "Gamma Adjustement".
The Fullscreen resolution it's adjustable on the Video menu too, but have custom values for CPS1/2 vertical or horizontal res. games and also for NeoGeo. If you don't like any of the predefined resolutions, open "WinKawaks.ini" with a text editor (Notepad will do), then change the bold text below
; This is the resolution for non rotated Capcom games
HorizontalFullScreenWidth=1024
HorizontalFullScreenHeight=768
; This is the resolution for rotated Capcom games
VerticalFullScreenWidth=1024
VerticalFullScreenHeight=768
; This is the resolution for NeoGeo games
FullScreenWidthNeoGeo=1024
FullScreenHeightNeoGeo=768
You need to choose correct values for you video card and monitor. I think it's self explanatory.