This would be flagged immediately. Law enforcement cameras check the plate against the registered make, model, and colour (which are public record in the UK)
Just pick up a plate number that matches your car; it's not like every car is unique. (But of course that would be harmful to the rightful owner of that registration number.)
Also, it's a little doubtful colors can be recognized in all light conditions (at night, in a tunnel, etc.)
And if the car is simply parked (vs. a road check), does it matter that it's "flagged"? What could happen? There would have to be a warning somewhere for the car to be impounded, or to send officers to wait for the owner to show up. Very unlikely IMHO.
Yes, actually, although generally speaking it's not widely enforced. Generally you won't get caught as long as the color on the registration matches the factory color in the VIN database, but you are supposed to ensure the vehicle description is accurate when you renew your registration and providing false information is a criminal offense, so if the color changes, you should update your vehicle registration.
Family member of mine actually got in trouble because the dealership typed the wrong color into the registration paperwork. The color on the registration didn't match the actual color of the car therefore it was considered illegally registered and the car was impounded during a routine traffic stop.
Also, it's a little doubtful colors can be recognized in all light conditions (at night, in a tunnel, etc.)
And if the car is simply parked (vs. a road check), does it matter that it's "flagged"? What could happen? There would have to be a warning somewhere for the car to be impounded, or to send officers to wait for the owner to show up. Very unlikely IMHO.