It happened with a roll that was developed with a cross-processed roll - I think that did something to the dev. But that wasn't that bad - just a bit greenish. I had a very green roll, though, that was from a camera that I left in my car all summer (gets about 50 degrees celcius in there) - and that film was also expired.
Please check your other thread as well. An additional possible cause of this is using a red safelight when handling c41 film. Undeveloped C41 film needs to be handled in the dark for obvious reasons.
Mild fogging will often produce this color -- it will print as orange or yellow and is the "trademark" color of mild light leaks. Darkroom not quite dark?