Color temperature is defined as the absolute temperature (expressed in Kelvin units) of a theoretical black body whose chromaticity most nearly resembles that of the light source. That being said, I believe DOT approved light is 4000k-4300K (rating used by majority of oem sources). I believe 4000k-5000k produces the whitest light, anything above that starts turning blue then purple.
For HIDs, street legal is 4300K (5000K on some BMWs). There is no kelvin rating on halogens because there is really no difference between them. They're all around 3800K. Ricer bulbs claim to have higher kelvin, but it's not true color, just yellow light showing through tint.
As for brightness, H7s legally can only be up to 1500 lumens, which is pretty much the max that can be produced off of 55W. Most normal bulbs are a bit lower than that, usually 1350-1400. No white/blue/purple halogen bulbs come even close to that because of their color tint.