It depends on the hospital and it might also be regional.
At the hospital I go to in California, green is for surgery and everyone else seems to be in a free for all. I know they reserve dark red for visiting specialists, but the doctors and nurses both wear whatever they want.
https://www.workwearexpress.com/blog/NHS%20Uniform%20Colour%20CodesI don't think there's a rule about it though, it's just what they stock & launder. I don't think they're mandatory for doctors at all – my understanding is they pushed to be allowed to wear them during the pandemic, at least at the hospital she was at at the time, and it just stuck, 'nobody' wanted to go back to 'professional clothes' and washing them at home, and it'd be hard to enforce once you've dropped it I imagine.
Edit: see this doc (2024), seems it's being standardised nationally, and there's nothing for doctors at all: https://azuksappnpdsa01.blob.core.windows.net/datashare/NHS-...
(So what they'll do in practice, no pun intended, when the trust moves to this system I have no idea... Keep using the old ones washing them at home? Buy Figs etc.? Stop wearing scrubs?)