Yup, just make the whole thing black. It's easy for even us non-artist types to color like that. *s*
You can get fancy and put black in just the original image white areas. But with it all black you'll get the original .bmp colors instead of having them blended with the button color.
>Can you specify what you mean by "all"? I'm guessing you don't mean to have the entire bitmap completely black, although I suppose it's possible you mean that. Do you mean to colour the white parts black, or the colour parts black, or what?