I am trying to colorize a mesh for a 3d illustration, and I have been using Steven's technique so far.
The problem is that, as Stephen notes at the end of his answer, the contrast between the two materials is rather sharp.
Is there a way to blur or gradient the line between the two materials?
I was thinking about colorizing faces with a ramp between the two different colors, but that sounds complicated, and I'm using Cycles, so maybe there's another, simpler way to do this?