My family used to play a similar game on road trips called "yellow car".
Each yellow car you call = 1 point.
Each purple car you call = 2 points.
Commercial vehicles don't count and put you in the penalty box if you accidentally call them, which means you must wait until the next person scores to play again.
Pink cars = Bonus round: Next car is worth double points for anyone, or triple for the one who spotted the pink car.
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We have recently modified this to a Camaro version since I ordered my car...
Call a 5th Gen = 1 point.
Yellow 5th Gen = 2 points.
Green 5th Gen = 3 points.
Call a Mustang a Camaro = Lose 2 points.
Call a Challenger a Camaro = Lose 1 point.
Any other foul = Penalty Box.
Only way to get out of the penalty box and play again is to spot a Camaro from another generation (i.e. 4th gen)
Great fun for roadtrips, but consider making a rule that the car must be in motion to keep people from scanning parking lots or dealerships when their eyes should be on the road!