Your sun itself is very pretty. They do like to have option of hiding . Even a tank background of solid color like black (thats just my preference) will make him more outgoing .
The gravel looks nice imagine its natural river gravel?
The kind I got it looks like Pea Gravel. I just got home from piano and he is real dark and in the corner. Is he adjusting to the new gravel? Or is it something else...
If you rinsed out the new gravel before adding it than he is just adjusting to the change and the disruption.
I find native fish more delicate than most tropicals . I dont have any now but had them as a kid.
Most sunfish need hide areas . If you add one or 2 nice plastic plants you will have great cover for him and his colors will look even better as he feels calmer.
He has turned back to his white color like in the earlier picks. Im gonna add some big wierd plastic ferm thing to it tomorrow. I did rinse the rocks and the log thing with water before they went in the tank