There where two versions of the plasma rifle on Halo 2, there was a blue / purple one, like the current plasma rifle on Halo 3, and there was also a Brute Plasma rifle, which was a nice deep red / crimson colour. Unfortunately, Bungie removed the Brute plasma rifle with the release of Halo 3. Hope this has answered your question Cameron (: The red one returned in ODST. Aidan :)