At the pet store I bought him they had HORRIBLE conditions for the animals, but theirs are still BRIGHT green, I bought one from there just to save the poor guy and he isn't bright anymore, he's always a dull yellow/green.
Colloration off the animals can change a lot. Bright and intens collors are often a sign of stress. My senegals also weren't bright collored all the time. But I see you took a pic outside a terrarium. As almost all chameleons senegals are not pets to handle a lot. I think this is not really good for the condition of your animal! I woukld advise you to keep him/her in his terrarium because in this way you don't give a much better life as in the petshop.
Looking at the eyes the animal is either stressed or dehydrated so please give it enough water.