Toss up between Yellow and Green. Both would feed my curiosity pretty well. I would love to know how bees and bats perceive the world, but Yellow would let you know how another human perceives the world. Another great thing about Yellow would be that no one would ever be able to figure out you had it unless you told them, and you could use it any time (unlike invisibility.. which would have practical limitations).
Grey would just make you atrophied and sickly.
Pink might make you a God, but I wouldn't want that kind of attention.
I'm assuming flying would mean that you are vulnerable to a surface-to-air missile. Besides, people can already sort of fly. Skydiving, hang-gliding, that flying squirrel suit (don't know what it's called), not to mention powered aircraft.
Phasing sounds good. But I went off on a random tangent as to why I actually chose it.
Random Tangent Included
Purple, the perfect blend of the active red and zenned out blue. Purple says action with wisdom and thoughtful planning. It's the colour of royalty and of violets the scent of which is curiously found mostly in the root of the palida iris, Irone and Ionone. How I love those two words. I can stare at the colour purple and fail to get any kind of eye fatigue and for reasons unknown it makes me feel calm and steady to do so.