Two Tone Brush?

I was wondering if there was a way to create a brush that half was the foreground color and half was the background color...

for example, I have a mountian brush. and the shadow of the mountian is black, as is the outline, but alot on the inside is white. Since its white, when i use the brush, if they overlap, you can see through the mountian... not exactly what i was going for. So, any way to use 2 colors? or make the brush sold without making it all back? I tried a shade of grey, but that just creates an lighter opacity of the forground color, and the FG/BG jitter just chages the color of what was originally black.

any ideas?

Nik

nope, but corel painter is awesome with that