My first chams were Senegals and I think they are delightful little chams.
Everyone perceives colors somewhat differently and there must surely be some slight color differences between individual chams, as well.
What the author describes as brown may appear more orange.
The chart listed in the first link is rather extensive, so there should be some coloration and pattern which closely matches your cham's--taking the above into account.
Senegals are generally wild caught and can arrive bearing a burden of internal parasites.
The stresses of capture,transport and captivity can cause a normally tolerable number of parasites to become more taxing on their bodies, even overwhelming.
This might be what is going on or at least a part of it.
Parasites can be eliminated but it requires medication that targets the specific type of parasite or parasites.
How is he otherwise?
Active? Feeding well?
I know that people often feel that cutting and pasting the questions from
https://www.chameleonforums.com/how-ask-help-66/ and then adding all their answers is a real pain or waste of time but it can be a great way to ensure that nothing is amiss that can be affecting your cham's health.