Wattage makes a difference in the color as well. 35W kits are going to give you the "truer" color of the Kelvin rating. 55W kits tend to wash the colors out some. Also, quality of the HIDs matter in determining the color, but as a general rule...

2500K = 100% Yellow

3000K = 75% Yellow, 25% White

4300-4500K = 75% White, 25% Yellow

5000K = 100% White

6000K = 75% White, 25% Blue

8000K = 50% White, 50% Blue

10,000K = 25% White, 75% Blue

12,000K = 100% Blue

These are based off what I've commonly seen, and may not be 100% accurate. Also, if you want my honest opinion, anything past 5000K does hinder the performance of your lights. I've owned several different kits in my time, and found that even 6000K didn't offer optimal lighting. I personally prefer 4300-4500K bulbs at a 35W rating. This way, you have the best visibility, the color of the light is not distracting, and the light won't be AS blinding to other drivers.