The colors are "liturgical colors," though I'm puzzed as to how they're managing white on your calendar! If you went to Mass on that day, the priest would be wearing the color you see on your calendar. Green is the color of many, many Sundays of the year, Sundays called "Ordinary Time," because they are not part of another special season. Violet is the color of penitential seasons:  Advent and Lent, to be precise. Red is the color of martyrs. When a martyr, such as St. Stephen on Dec. 26, is celebrated, the priest may wear red. White is the color of virgins (at weddings, it is meant to symbolize the same), so the feast days of virgins call for white vestments. I don't think I've covered every possibility, but that gives you the idea. Sounds like a nice calendar! My parish calendar is at home, but I'm going to see if it has those colors as well.