Please note this list is not exhaustive - if you feel you are close to a foundation shade that doesn't match your undertone, then go for it! You know your skin best.

N1.5 - Very light skin with a neutral undertone
N2 - Very light skin with a warm undertone
N2.5 - Light skin with neutral undertone
N3 - Fair skin with a warm undertone
N3.5 - Fair to medium skin with neutral undertone
N4 - Medium skin with a warm undertone
N5 - Medium skin with a warm undertone
N6 - Medium skin with neutral undertone
N7 - Medium to dark skin with a warm / neutral undertone
N8 - Medium to dark skin with a warm undertone
N9 - Medium to dark skin with neutral undertones
N10 - Dark skin with a warm undertone
N11 - Dark skin with neutral / cold undertone
N12 - Dark to deep skin with a neutral undertone