What is the brightest hid color?

The lower the color temperature, the higher the light output. But this doesn't really matter. There are about twelve different legitimate HID bulb types: D1R, D1S, D2R, D2S, D3R, D3S, D4R, D4S, D5R, D5S, 9500 and a few others. They all produce about the same amount of light (around 3,000 lumens), and they all produce light of about the same color temperature (4100K to 5000K); any nonstandard color temperature or lumen output is illegal. The differences among the various bulb types are physical and/or electrical to work with different kinds of headlamps and different kinds of electrical control gear. The end user does not get to choose which type of bulb to use; that decision is made at the headlamp design stage—each headlamp accepts only one kind of bulb, and putting in the wrong kind ruins the safety performance of the headlamp.