I don't know what it could be offhand.... But that 'bumblebee' looks like it has some sort of darker gene in there as well. The head is still so dark and I feel like overall the snake isn't as bright. It can also explain the 'nice normal' the Banana looks like maybe whatever that gene is may be at play as well?
I agree on the spider bananas. For a 100% ID, take a mag light and hold it to the forehead of the snake like you're candling an egg. For a BEL morph, the pupils will shine red. For banana or coral glow, the entire eyeball will shine red.
Gorgeous surprise regardless! I wish I could be more help.
Thank you both for the replies. Very generous surprise indeed!
The dark gene, could it be mahogany?