I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
It could be due to a lack of good sunlight. Otherwise I am not aware of anything that makes a blood banana lose its red color. I think it will return if the plant is getting enough sun.
Thanks for the question. Please stop in again soon!
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