次のようなクエリが必要です:
SELECT * FROM car
INNER JOIN car_color ON car.id = car_color.car_id
LIMIT 1 -- this will limit the results to only one row
編集:グループを使用できる車の色を1つだけ取得するには:
SELECT * FROM car
INNER JOIN car_color ON car.id = car_color.car_id
GROUP BY car.id -- this will group all the rows with the same car to only one row per car