Banana plants do respond to light and that threshold can be quite low. The absence of light and shade are different, but it is easy to observe a banana bloom opening between dusk and dawn. The last photo was dawn on October 25, 2012 and I'll look for the October 24, 2012 dusk photo.
Originally Posted by Nicolas Naranja
They turn dark red in response to light. There is likely a threshold. I imagine that if you put a bunch in a black or reflective bag you might get the greener red coloration.