Are you just going to paint the whole thing yellow? If so I would recommend an acrylic paint. I have never heard of any problems with heat dissipation, unless you're planning on trying to run a 500mhz at about 2G. If you're that concerned about it just put another case fan or 2 in it.
If you're any kind of artist, paint some sort of design on the case... that makes it more of a conversation item.