OrSony is right, bulbs that is rated 14-15k are usually white and can be seen yellowish like a 10k color. But it still depend on the brand as Reeflux 12k is bluish.
Ballast plays a part too. Magnetic ballast will have a stronger drive which make the bulb more whiter else a eballast has a weaker drive which make make the bulb more bluer.
So if you want to get a bluer bulb, I suggest u get the Radium 20k, which most hardcore sps users are using it now
My 2 cents