My Cats Eye Is Discolored. What Could It Be?

The cause of discoloration depends upon the part of the eye that is discolored.  If the sclera (white part) is red this is a sign of irritation and likely conjunctivitis.  If the iris is discolored it could be a benign change or possibly iris melanoma.  If the lens is discolored this could be nuclear sclerosis or a cataract.  If the front chamber is discolored it could be pus or an inflammation in the front chamber of the eye.
As you can see there are many possibilities.  This eye should be looked at by a veterinarian.