The color k-meleon uses for menus is AFAIK the system set color for all programs.
This limitaion is the price for using the native windows widgets.
You can only use Your black bmp and try to change the windows settings.
They can AFAIK not be changed in the .jar files. K-Meleon uses no XUL for the themes. Altering classic.jar or influencing it via a userChrome.css would only alter XUL pages like about:config & about