By "this" I meant the totality of what they did, not certain bits among what they did that can be "think of the children"d (recognizing that I've now given someone the opportunity to interject with a bad faith interpretation of that).

There's no basis for saying you have to get rid of a blue based color theme for a grotesque swamp green one, otherwise PayPal would be an accessibility pariah.

I probably shouldn't be so sensitive to this, but it's part of the ongoing theme in the tech sector of snatching the lolipop from the baby. Give it, let them enjoy it for a while and get used to that, then spoil it.

But fixing this certainly would not require a complete and total redesign, or?

No it wouldn't, but it is what the article's about. Maybe the link was changed, but I'm only aware of the 'complete and total redesign' from comments here - I've used Wise occasionally but not since it was called TransferWise I don't think, so I wouldn't have known it was so recent.

Isn't color blindness mixing up red & green?

So why would a green design be better than a blue design? Naively, it's strictly worse.

You're right, that is naïve.

'Mixing up red & green' is one type (or a trait of some types), not the only one, and it doesn't mean say 'RGB' spans only two colours - it means some shades of red appear green and vice versa. It can also depend on context (red laser pointer invisible over a sea of green, say) and knowledge of the difference (presenter says something about their red laser pointer).

There's no problem with using green, it's requiring it to contrast with red that's potentially problematic. For that reason it's probably a good general theme/background colour, even if that was the sole reason they were choosing one, because you'd be unlikely to want a contrasting red text colour over green background anyway.

Still doesn't explain why green would be better than blue.

Don't all problems go away if you're just using blue?

it's not about choosing only one colour, colour blindness and colour systems are more complicated than that.

If you see the image under the "Double the tests, double the success" subtitle you'll see that the blue colours were actually failing a few of the APCA tests for colour contrast.