[bambax]

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.