I just got a two year old Oscar fish on Monday. I know the basics of taking care of him and I've been trying to make sure he is happy and comfortable. Today i was checking on him and his back seems to be turning a purple-ish color and I'm very concerned! HELP!

Firstly welcome to the site

Have you tested your water? And is your tank cycled

Fish do change color for various reasons, most of the time it's nothing to be concerned about. However, fish that become ill often lose their color dramatically.

You need to check your water and then we look at the situation a little more

Let's hope it's just the colourchanging Oscars can do when stressed or sulking!
Mine can turn pale in a matter of seconds, but will change back within a short while...

Yeah mine two will change colour from black and gold to green and white strips with gold. All at the drop of a hat but mostly with they fight.... every time the dorsal fin goes up...the colour changes, and back again in a second. It looks really kool I reakon.lol

Colour changes can be perfectly normal, however there is usually a reason. For example 2 oscars fighting will often change colour or if an oscar is frightened (like being put in a new tank).

However they can also change colour if they are not feeling well. If your tank is not cycled then you will have ammonia and maybe nitrite present. Can you post a test result for ammonia, nitrite and nitrate. DONT use those test strips as they are very unreliable, please use the liquid test bottles to test your water. How long have your tank been running for with fish in it. Also how big is your tank?