I do more than one tree and I do them all differently each year. The main tree in the living room, I'm thinking of doing just a red and blue ornament theme with clear lights. I've never done a red and blue tree. Sometimes I end up adding a 3rd color and if I do it might be white. I might buy some blue lights to add to my prelit tree with clear lights. Last year I did the copper and brown colored ornaments and I really liked it.
The tree in the basement might get mulit colored lights with gold and silver ornaments, not sure about the 3rd color. I will see when I get out my decorations. Sometimes my plans change.