Like it says on the rules:
Maximum Textures
1024x1024 Diffuse
1024x1024 Specular (optional)
1024x1024 Bump / Normal (optional)
1024x1024 Alpha (optional)
1024x1024 Glow (optional)
The diffuse aka color is the only texture map that isn't optional, so yep, you haveto texture it, I don't think there would be a problem if you and your mate worked on it, it doesn't state in the rules anywhere, but you'd haveto fight for the prize
.