The G3 Gundam is simply a colour variation of the RX-78-2, this colour
scheme didn't appear in the anime but was mentioned in the original novels
by Gundam creator Yoshiyuki Tomino.
I originally created this image in Cinema4D SE and it was one of the
first pictures I showed on the internet, recently I re-rendered it in
Cinema4D XL6 which is a much more powerful program. The chief difference
between the two images is the blade of the beam saber, C4D XL6s "tube
light" function making it much more distinct than the original which
was cobbled together using three seperate light sources.