Apologies if there was some confusion on my comments here, by no means were they to be dismissive in your thoughts.
Whilst it’s been discussed today and in the past, it’s also been addressed as @Revels posted here:
It looks to have also been raised via the Apple community a few times:
With responses directing to raise it via Apple feedback, and the latter post saying with your bank (it’s been raised a few times over the community, and likely from customers via chat)
I understand it’s not the answer you were hoping for, but Monzo is always looking for ways to improve or implement new products or services.
This would be cool, but save the time consuming process, colour would be representative of your account type/main card type.