They tend to show ultra bright colors when burned slightly. My melleri had glowign while on his back when he was burned 2 years ago. It took nearly a year for the tissue to fall off - including a substantial amount of his spine. Melleri lose their dorsal crest and lobes easily when burned. Other chameleons seem to just regrow the skin after a few sheds. Male veileds will often have glowing yellow/green spots where they've been burned.
If it's a bad burn, it will probably turn black in a few days, scab up, crust over, fall off, maybe regrow... if it turns black, apply silver sulfadazine cream (get it through the vet even if it's NOT a burn - you'll need this stuff eventually). Unless there IS an infection, it's best to just use topical antiseptics. Preventative anitbiotics in chameleons suffering from burns is (In MY opinion) not worth the risk. every burned lizard I've had recovered without infection, with a treatment of topicals only.