What I've seen:
- White or Red for Pascha. I don't see much debate beyond this; red is a traditional Paschal color (think eggs), as is white.
- Purple for Lenten weekdays & Holy Week. Some traditions (certainly not Greek) use/allow black during Holy Week, a practice that I strongly disagree with.
- Red for Christmas. I think I've heard of using another color, but I can't think of it.
- Blue for feasts of the Virgin Mary. Some wear blue for Theophany, some red, some gold.
- Gold as an "everyday".
- Green for Pentecost seems very common, as is Green for Lazaros/Palm weekend.