my turtle is turning red!

So i havea red eared slider, and around the edges of the belly, its starting to turn a bit orange-red. and the a little bit of orange-red on the top of the shell as well.I had a trurtle a few years ago that died and the belly was almost like a blood red, and i still dont know what happened to it... It this orange-red color natural? or is there something wrong with my turtle?