Change highlight/shadow colors on grout lines?

[rmccoy]

I am trying to figure out a way to change the colors of a material to where the sections that are hit by light show as a shadow and the shadows show as being hit by light. I basically need the colors to be inverted when rendered. The reason I am doing this is because I am doing the grout lines in a building as a positive instead of a negative (renderable spline). I've attached a render showing what I am working on. Thanks in advanced for any suggestions.

[Chad Warner]

Depending on how close you are going to be getting, I'd just make the material a darker version of the field color and call it a day. Just turn off cast shadows, and it'll work pretty well as a renderable spline.

[rmccoy]

Thanks for the response. I think your idea sounds good. I won't get too close so it really doesn't matter all that much. The perfectionism was kicking in a bit lol.