HAHA!!! good call, i doubt it though. wasnt EVER reddish. It was pretty big until i had a huge problem w/ bba, so trimmed off the much larger leaves. It's derived from my uncle's batch of sword plants which are all amazon swords.
Unless its going from green to red, to brown, you don't need to worry.
My best guess is that it is a melon (as adz said) or flame sword. Maybe your fertilizer, co2 or lighting was increased or recently added which triggered it's colours. This would mean you're doing better than you had been before, it's a sign of good progress.
When did you start fertilizing? I know tropica master grow does have some DTPA iron in it, I believe this would be your variable that caused it to go red. It's happy.