Impossible to say for certain without seeing the fish, but it could just be normal colouration; all my blue platies had a bit of red/orange on their fins.
Standard questions, to check on the fish's living conditions; how big is the tank, how long has it been set up, what fish are in it, is it cycled and have you tested the water at all; especially for ammonia and nitrite?
Without seeing anything, I'd throw out that its probably just its natural coloration. Orange platies are pretty common, and platies (and swordtails which they interbreed with) don't care about color morphs when it comes to breeding.