If I have to pick all one color I like blue. Too many people do white. And while I like those icicle lights - they are just everywhere. Blue seems very much better for just simple roofline thing. But, if doing up the whole place - I like lots of colors. Not that I've ever done the outside.
I've always loved the blue ones. My first year away from home - in Germany - I bought a little artificial tree (we weren't allowed to have real ones in the dorms) and did it all in blue. It was gorgeous...IMO, at least!
I just have a problem with EVERYONE using icicle lights. Boooooring!
There's a family at the top of the hill near my house that has a lovely display...they have a big border of trees around their house - little trees, bushes, really, about four feet high. Each tree is a solid color...a whole row of different colored trees. I like that a lot.