hid lights question

i have a 2008 equinox, i nistalled hid lights 6000k about a year ago. now one is starting to look a bit yellow. it has hi/low beam. would it be the buld or the ballast. if the buld can i replace both of them with and hid lights or does it have to be hi/low too.
tom

If the bulb is changing colors, it's a bulb problem. Not sure what you are asking in the second part of the question. The bulb should be replaced with what the vehicle calls for.

i ment do i need to replace with hi/low or any kind and can i also put 8000k instead of 6000k or do i need a whole new set, ballast and blubs and what are the best that will not go like yellow and last longer thyan a year

I have the same car as well as hid's. I had the hi/low bulbs at first and replaced them with 6000k non hi bulbs. You just dont have a hi beam thats the only difference. Dont go cheap with the bulbs! You get what you pay for.