Honestly, I wouldn't try to match the pool water color. I wanted a blue pool and thought a blue waterline tile would help. It "matches" sometimes, in certain sunlight angles and sky conditions, and sometimes it doesn't, and sometimes I think it downright clashes with the pool color.
If I had to do it again, I'd choose a complementary tile, and probably a really bold tile to really jazz it up. I'm searching for backsplash tile for my kitchen, and when I see the really neat stuff that tile designers have done for pools, I'm really impressed. I'm not talking abut Mastertile or Luv Tile or the standard pool tile companies.
And really think about a mosaic, maybe talk to people who have one. A contractor friend who has two pools advised me not to get a mosaic type waterline tile because it is more work. We have hard water here, so we have to scrub our waterline pretty regularly and that's a lot more grout. Plus any variation on water level is glaringly obvious...our next door neighbor has the diamond dolphin in the middle with the four corner pieces and it makes me crazy when their water is low, plus it's really obvious that their pool is not level.
Just some things to think about. Good luck!

Thank you c9pilot. That is a huge help. I just dont know what color to do. I have to make my mind up SOON. :( It's a mid century modern home and probably should be minimalist colors. I have hard water also, but just dont know what type of tile to use other than mosaic.

With Gray concrete coping and white plaster I would suggest going with a glass tile for the pool and spa to 'jazz' it up as c9pilot suggested. Your builder should provide a wide range of samples for you.