A priest might also wear a zuchetto (the skull cap that you see the pope wearing). Priests and bishops are entitled to a gallero (a big, fancy hat - like Fr. Guido Sarducci wore) with long tassels. Occasionally, you do see a priest or bishop wearing a biretta.
Priests wear black hats. Bishops wear various shades of red from something more like a purple to scarlet. I forget what color monsignors wear. Pope wears white.
Mitres can be various colors, similar to regular Mass vestments.
