If you right click on the part that lets you set the color you will get a context menu asking "use expression.
You can click that, and in the in the box put the expression rgb(r,g,b) with the r,g,and b in parenthesis set to your color.
After that you'll need a counter something like:
rgb(r+variable,g+variable,b+variable)
add 1 to variable
You'll want to add to the values as rgb(255,255,255) equals white, and rgb(0,0,0) equals black.