次のようなクエリを使用できます:
SELECT
id,
SUBSTRING_INDEX(SUBSTRING_INDEX(colors, ',', n.digit+1), ',', -1) color
FROM
colors
INNER JOIN
(SELECT 0 digit UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3) n
ON LENGTH(REPLACE(colors, ',' , '')) <= LENGTH(colors)-n.digit
ORDER BY
id,
n.digit
フィドル