Why do my bananas ripen to a white color?

My family purchases about 8 bananas a week from our local grocery store, and we let them sit to ripen for a day or two. When they taste perfectly ripe, the peel is very white on the top half. I have asked about other peoples' bananas, and nobody has the same experience. Could it be from the location of the bananas? (They are near a window next to the sink. Not in direct sunlight. They are also hung rather than sitting on a table.) Or is it some other reason?