This will show you how to make a Portal gun model from the video game Portal, using lego. (no it doesn't work)
It features interchangeable colors, blue and orange. (step 6)
The steps are in the photos. I have highlighted the pieces you need to add with each step.
Includes optional stand. (step 5)
See also: http://www.instructables.com/id/Lego-Atlas-And-P-Body/