I want to paint the background of my gas fireplace (behind the logs) a lighter color so the logs and fire will be more visible. Do you know of a paint I can use to do this?
Yes. These are painted all the time. I just used this for a traditional wood burning fireplace. You can search for fireplace paint but really you are looking for it to withstand the max temperature. Since yours is gas I am guessing your max is well less than 1000 F.
Also most fireboxes are painted black so you can see the fire easier. And because of the heat a lighter color may get burn marks in it from the heat.