I read this somewhere on Specktra, sorry I can't remember the link.
Mac shades/Codes:
C= COOL, yellow-golden olive undertones
N= NEUTRAL, beige undertones
W= WARM, pink undertones
NC= NEUTRAL COOL, golden beige undertones
NW= NEUTRAL WARM, pink beige undertones
I use both NW and NC shades in Studio Fix powder depending on how my skin looks to me that day!!