yes, they do require a "warm up" period. although there is plenty of usuable light right when it is turned on, it typically takes anywhere from 10 -30 seconds for the bulb to stabilize and reach full/optimal brightness. when you turn it on, it's brilliant blue for a split second, then warms up to a pure white (what it's suppose to be). then there are some of us that seems to love that blue color from initial arc strike so buy blue colored bulbs (which looks kinda silly but i'm sure yalll already know how silly you look driving around with blue/purple/pink lights).

you can look at any stock car that comes from the factory with xenon and see that although the halo at the headlight might look real blue, the light on the ground is pure white (with the exception of the lincoln mark 8 and early 90's bmw 7 series, which happens to come with 6000k bulbs from the factory. they figured out that it wasn't such a "hot" color to drive with and switch to 4100k).