The supermarket here sells the usual Cavendish bananas but they occasionally stock other varieties, including the popular "emperor" bananas (small and sweet bananas with thin peel and little thready fibre) which you can find across Asia. Red bananas, on the other hand, are relatively more exotic (at least for me in Hong Kong). The supermarket here labels these as "Moroccan red bananas" but it seems that these are grown in Asia as well.
As for the flavor, they're a bit firmer and less mealy/mushy than regular Cavendishes. While they're still sweet and have the familar banana flavour, I thought the red ones had a little more tartness and complexity to them which I don't find in the normal yellow Cavendish.
Have you ever wondered why you can buy different kinds of apples, pears, potatoes and melons, but across the (developed) world, you usually can only buy one kind of banana (the Cavendish)? The reason for the domination of the Cavendish banana in supermarkets is mainly because of its hardiness/ability to withstand long-distance transport and ease of propagation. However, the whole banana issue is pretty complex - when you are dependent on only one single type of banana, you render the commercial crop vulnerable to pests/disease [viz. the Irish dependency on potatoes that caused the potato famine in the 1800s]). Also, the Cavendish is a relatively bland flavour, but it is popular because it is easy to ship and keeps for a long time. This means that consumers have sacrificed variety and taste in favour of convenience and mass production.
I find this kind of social info pretty fascinating because I believe that we take so many conveniences for granted in our 21st century lives.
For example, in Hong Kong, Sunkist oranges from California still dominate the market, even though it would probably be simpler and more cost-effective to buy fresh oranges grown in Asia/closer to home. Also, how can oranges/apples/strawberries shipped thousands of miles across the Pacific arrive in stores so fresh and sold at such a relatively low cost? Oranges from California at 40 US cents each? Apples from Washington state for US 30 cents each? I suspect that some of these costs, e.g. pollution and waste, is being passed on to the public and on to nature and is not being reflected in the supermarket sticker price.
And why doesn't China start growing high-quality perishable fruits such as strawberries, blueberries, and other "Western" fruit? I'm sure there is a huge market in Asia for reasonably priced "luxury" fruits. I would totally buy blueberries grown in the region rather than blueberries flown all the way from Chile (which is what you currently get in the stores here for US$0.60 - $1.20 per 125g carton - how can they sell them so cheap?!).
Actually there are many types of bananas: at my parents' home in Hong Kong, they grow the common banana (or "big banana" in Cantonese), which is fatter and shorter than the Cavendish. It's also tart with only a mild sweetness which I like as it's not overwhelming. The ones my parents grow also occasionally produce black seeds. When was the last time you saw seeds in your supermarket banana?
Confession: my parents merely tend the banana plants, which grow wild in many places in Hong Kong. It's mainly transplanting the offshoots [bananas can reproduce by seeds which are genetically different or by offshoots which are clones] to avoid overcrowding, harvesting bananas and chopping down the trunks/stems to make room for new plants once the fruit is harvested as each plant usually only produces a single hand of fruit.
If you're interested in reading more about the commercial banana and the current challenge to the global crop caused by an infectious fungus, I highly recommend a recent New Yorker article from January 2011 by Mike Peed: We Have No Bananas (Scientists fight a devastating banana blight) -- subscription might be required but you can see a related short video for free on the magazine's Tumblr site (also pretty interesting).
