KJ, banana ID is indeed murky. As someone who teaches taxonomy, albeit of fishes, before knowing anything, I thought it would be pretty easy to distinguish different bananas. For some varieties, that might be the case if you have a plant that has flowered and produced fruit. For others, you'd be lucky just to get it down to subgroup. Gabe has written a good description of the complexities of banana taxonomy that you can find on this website if you search a bit. For people like him, who have seen a lot of different bananas, banana ID is easier than for relative novices like me, but with 1000 or so varieties, there are a lot of cultivars that even the experts would have a hard time identifying.
The fact that environmental conditions can change characteristics that seem like they should be important (like color), certainly confuses the issue. For example, sometimes my ABB varieties (e.g., ice cream, orinoco, namwah) have pink midribs and sometimes they don't.
If you are interested in learning how to distinguish different edible varieties, the following document by Jeff Daniel's is the best one I've found on the internet. You have to download each part separately (and ignore that fact that it looks like you have to pay for it). It is focused on South Pacific varieties and so it leaves a lot out, but it has good info on separating AAA varieties from AAB, from ABB, etc.; and gives important traits that help distinguish some varieties within these groups.
Illustrated guide to the identification of banana varieties in the South Pacific | ACIAR