the most useable of the kelvins mentioned above is 4300k anything above 4300k-4500k you start to lose lumens . 4300k is around 3100 lumens 6000k is around 2700-2800 lumens. the farther you go up less actually light output there is..
all stock cars equipped with hid's are between 4100-4300k.. every oem hid application is either a philips or osram (slyvania) bulbs.. the flicker of purple and blue isnt from the bulb but from the actual projector itself..what you are witnessing is the cutoff flicker from the hid projectors. i suggest anyone looking into hid or hid retrofitting to take a look at http://www.hidplanet.com and look at there forums