heres the only bit of advice i can give. it may or may not help the situation.make sure the cage is drying out between sessions, make sure you have the right temps basking and ambient, you could dab the site with a little provodone iodine diluted with water to a mild tea solution with a cotton swab after it dries put a little antifungal cream on it or polysporin if you think it is not fungus.
again i truely have no idea what your chameleon has and my advice isnt going to hurt your cham in anyway but also may not improve the condition.
ive only personally seen that webbing at the base in a fugus case one of my melleri got. the site was yellow though not white.
Just out of, curiousity, has your cham recently shed? it could be left over skin that just hasnt come off. Not saying that what others have said is wrong... just wondering.