colorid = sign(DataMatrix) + 3; %negative -> 2, 0 -> 3, positive -> 4
colorid(isnan(colorid)) = 1;
Now nan are 1, negative are 2, 0 are 3, positive are 4. From there you can create 4 x 3 color table such as
colortab = [32 32 32; 0 128 0; 256 0 0; 0 0 0]./256;
image(colorid)
colormap(colortab);
