When you turn your wrist over or palm over (to the white meat, lol) look at your wrists and tell me if you see more Yellow or more Reds. That's your undertone color.
For Mac if you see more yellow, go with NC, if you see more reds then go with NW.
Some, mostly of a middle eastern decent will see a olive/green complexion, they need the C formulation.
Some women that have very dark rich color, like my ex mother in law from Ghana Africa need the W formulation. Her tome was very red and deep dark and rich bu Mac had that color made just for her.
The C and the W are mostly found at the Pro Store.
Oh and I forgot to mention that I love foundation color pallettes. LOL, I have cheapies from Costal Scents and I have more costly ones.
If you are able to check out YT right now you want to look at Beauty Chameleon, I think her username is something funky like nhop79. Makeup by Ren Ren is pretty good too.