If you have rosy red cheeks (like me), it doesn't necessarily mean you have a pink undertone to your skin. I just got matched by Estee Lauder to find I'm a 1N2, when I thought I'd be a 1P2.
Always match to the neck, so I'm told, but yes, matching up to a colour chart online is near impossible! I have so many foundations to ditch/sell from not getting it quite right!