Select the polygons you want to be a different colour and assign a different material ID.
Check the tutorial on how to this.
http://en.lfsmanual.net/wiki/3D_Render_Tutorial
You'll want the 'Rims Mapping Correction' section and read on from there.
Check the tutorial on how to this.
http://en.lfsmanual.net/wiki/3D_Render_Tutorial
You'll want the 'Rims Mapping Correction' section and read on from there.