I thought I'd share my way of blending colors, since a lot of people have been asking how I do it.
It's kind of a simple mans blending, because it doesn't involve mixing colors.
As an example I took the arm of a cybot, painted in the Dark Angels theme.
This example is very old, so it might not be the smoothest result, but it should be enough to give you the general idea.
For this arm I only use 2 colors and a wash: Dark Angels Green and Thraka Green Wash as a base