Green Spotted Puffer color changes

Question
Hi! My green spotted puffer lives in a 10gal brackish tank (soon to be 100gal marine) and every day about he goes from a black belly to a white belly. Is this caused by stress or any sort of disease or is it just something a puffer does? Thanks in advance!

Will

Answer
WIll
     Green Spotted Puffers can and will constantly change colors when they are healthy and happy.  Their belly will change from white to black, and their backs will often change from dark green with deep black spots, to a very light green with pale spots.  If they don't change colors, especially if they stay black, it is usually a sign of sickness.  Hope I helped. Good luck with your new tank.
                                         -Brian