Have to mention I was too poor/tight to replace the Mercier TM this week and went to Boots for a budget replacement. The lady on the No7 counter zapped me with their new machine and listened to what I wanted (a good coverage tinted moisturiser) and said my colour was warm beige (usually Nude for LM) and sugg their Essentialy Natural very lightweight foundation.
Bloody hell its good, because I was zapped the colour match is perfect and its so light you can't see it at all or feel it, it just evens out my face.
Try the service, particularly if you have a drawer where you put your foundation mistakes (ie Bourjois Healthy Mix Serum no 52 like putting on a Caspar the friendly ghost mask for me)