I picked up a lot of well loved Mags recently and I got a few rare C cells in the bunch. They aren't in the best shape, they aren't super rare, they aren't worth a ton of dough, but they do work and the price was right!
Colors on C cells are rare as the C cells were very slow sellers and Mag just didn't market them like the D cells. I've never been able to put together a complete listing of the colors produced and I'm not even sure there were an, aside from Vari-Beams, before 1988. The blue 3C above is a very cool light. It's a 1990 or 1991 "Transitional" model. It has the laser etched bezel that was only done for these 2 years before the Panther logos came out in 1992. It is serial ~812,000. This is pretty interesting because 3Ds form the same year were around 3,000,000 but 5 and 6Ds were around the same production as the 3Cs. Kind of shows how they sold compared to the other lights. They probably made a red 3C for a little while also because the blue finish is identical to the blue D finish and the Ds were also available in red and silver.
The green is the lime green version as Icarus showed above, although mines been used just a tad more. This was a special order color and I believe they were done for Home Depot since they sold so many lights. All of these seem to be from the late 90s and early 2000s. Any lime green models are tough to find now. They also did them in a 2D and 3D. I haven't heard of any other Lime Green sizes being produced though.
The purple was a standard finish and they do come up occasionally. 3D and 2D purple lights are still in production but I believe the 2Cs were discontinued a few years back. The C cells are only made in black now.
I've also seen 2C standard green and 2C silver but I don't own either. I have a 1988 gold 2C that's very rare as Maglite only put out a handful.Other than that I don't know of an other C cell finishes.