i got some acaras last week, they do the same thing. Radical color changes depending on mood and activity (feeding time, being intimidated, intimidating other fish, mood.) Cichlids are known for being that way. I like it, its like getting several different looking fish in one LOL. Alot of fish will change color when spawning too. Think of it like birds will show off fancy feathers for a prospective mate, same idea here with the fish. Lighting and substrate also will change the appearance of your fish .