I have medium auburn hair that is beginning to gray at the roots. I've been using Clairol permanent hair color and mix several colors to find a great color that's close to my natural color. What is the best strength developer to use to cover the gray? Also I know that reds/auburns fade quickly, but mine seems to fade and turn brassy very quickly. I've been using 30 developer. Is that the correct one?

I use 30 as well. I like L'oreal better than Clairol, though. It seems to hold the red longer.

You should be using 20... 30 is more lift and less deposit.