I’d recommend reading a couple of posts such as this one to discover why this is unlikely to happen in the near-term at least.
In short, these custom designs require very different methods of card production and are significantly more expensive than making many identical cards. It’s also worth noting that right now in the prepaid program, cards are produced in large bulk and mailed out to customers as required, this shortens the time to send out a card by already having them produced ahead of time.
The general thoughts seem to be that the benefits of being able to get a card to a customer the very next day outweigh the benefit and demand for this level of customisation.
I think the Hot Coral card colour has done the job of unique card branding, I’ve certainly had many people in shops note the bright colour.
One thing that doesn’t seem to be so strongly opposed is the idea of possibly offering a small number of different card colours. I know Hugo (Head of Design!) has mentioned this a couple of times.