g.fillPoly dithered colors

The g.fillPoly function is great, but I'm wondering if there's a way to fill it with dithered colors. For example, let's say I want my polygon to be filled with a black/blue checkerboard pattern. I tried setting the color to (0,0,127) like so:

g.setColor(0,0,127);
g.fillPoly([14,14,20,14,25,25,15,20]);

but it still filled my polygon with full 0000FF blue.
It appears that even (0,0,1) will show the same 0000FF color that would be expected from (0,0,255)

I enjoy the challenge of designing in 3-bit color, just trying to learn the best practices for this sort of situation.