Look at this, it might help you.
It has a list of common aquarium plants, some of them being reddish purple. Some don't have pictures, so you can copy the name and look.
I'm looking still to see if I can figure it out. :)
Where did you get the plant? It's possible it was missplaced and they put the wrong name on it, or it might not actually be an aquatic plant. But if that's the case, it would probably be one of those top fin plants in it's own cylinder. I don't think that would happen otherwise. Hopefully it is a true aquatic plant! It looks like it's doing well.
Here is another link to lots of aquatic plants (descriptions and pics):