Are the undersides of the leaves purple? Musa zebrina is actually Musa acuminata subspecies "zebrina." How did you come across this plant? Is it seed grown or a clone? If it is from seed, you can often find more variation than one might think. If a clone, then?? It sounds like you have changed the lighting to no effect. Mine usually get less purple color when exposed to bright light. Try to post a picture.
Steve

HI Cannaz,I don't know the procedure about posting pics on this forum,I have taken a shot but hope to find out somehow,the way to post it.It was grown from seed and it is colourless underneath.I have just read your page and I see you are growing a coconut,this is one of my lifes challenges I have now had about six and they are short lived,I think about six months is my best to date.I give it all the care it needs but still no luck,the leaves go pale and usually brown off at the ends and work downwards.How long have you had yours?I keep it in a conservatory in the u.k.with a winter min of about 60 degrees.My daughter unbelievably kept hers for 8 years and lost it while away on holiday when the temp was set to come on at 45 degrees,far too low.She is no great plant lover and the care routine she gave it was...a cup of water every wednesday and never repotted it!!.I give mine all the care in the world and fail.
Do