UNFORTUANTLY, YOUR PIC its to small for me to see, however consider the following....
check the bottom of your arms are they more pinkish redish or yelowish? also depending on the product u may either pull more yellow or pink, go to the mac counter and ask about the foundations figure out what u want first (coverege and so on) then ask for a sample of each if the mac artist isent well trained they may pic a wrong one for you. consider tryinng both (nc and nw)one on each side of your face, wichever turns orange is the wrong one. u will be able to tell right away especially if u step in natural sunlight, from the pic u seem like an nw15 but i may be wrong good luck!