I would recommend you fill out the https://www.chameleonforums.com/how-ask-help-66/ form and we will be able to tell you if anything needs to be changed about your husbandry. And also taking some photos of him/her and the enclosure. And I also strongly recommend reading over the care het that is in the link below. It will pretty much tell you everything you need to know. https://www.chameleonforums.com/care/caresheets/jacksons/
This is the third post on his color - you've never answered how old he is - how old is he ? Mine is 5 months old and has been brown since he was born- he gets greener before bed and has different shades of brown - If your not sure of the age post a picture- or post a picture even if you are sure of his age - Lots of people here have Jacksons and may be able to pick up a problem. There is another thread that has a Jacksons development in his first year - I'm pretty sure you're just worried about nothing but without answers and pictures it makes it harder for anyone to help-