handling depends on many things.
i personally feel that handling should always be on a chams terms.some people can handle there chams and some cant.patience is very important.
some people like me are lucky.my cham loves being handled but thats due to how he was raised but i never pick him up.he always comes to me or should i say grabs me lol
if your cham does not want you near him he will show it by either turning dark,running away,puffing up or maybe even hiss & lunge.as yours is turning dark then he is becoming stressed.you should leave him be and in the mean time build up his trust.you really dont want to stress him out.
you are a predator to him with big hands coming in.put yourself in his position.
you want him to feel comfortable around you first.
the best ways to do this are hand feeding.i also believe free ranging helps too but he may never like being handled,some just dont.
personally what i would do is just mist and feed him and leave him be for a few weeks.once he seems calm with you just doing that then i would try hand feeding him a nice treat.if he runs away or shows distress then move away slowly and try again the next day,just take it slow and enjoy your beautiful animal.xx