I'm not sure if I'm understanding the question, but the keyboards are matched to the body still. In the case of my M4 iMac, it's a very pale green for the keyboard and the magical mouse.
Ah, ok, now I understand. I would assume the accessories are perfectly matched to the iMacs they shipped with. I can't imagine Apple giving you a keyboard with the "M3" shade of blue when you buy an M4 iMac. They're incredibly detail oriented about this kind of thing.
Whether this would be very noticable in real life is another question.
OK, I'll assume the blue keyboards (mine is matched to the stand) changed as well. I ask because at some point I'd like to pick up the M4 blue keyboard with Touch ID, I bought the base M4 iMac with upgraded storage instead of the regular "upgraded" model.