It's about finding the best colours that enhance not drain your face, mask shadows etc. Cost is about £99 for a morning, after which you go away with a wallet containing the best colours for you, plus information about which of these are the best colours for you, and which are second best. There are reps all around the country, even down here in the bum end of nowhere :)
My experience - interesting, informative, not completely sold, as I was diagnosed as a vibrant autumn and can see some of it (no black, for instance, cream better than white for me, can now find a good yellow to wear in the shape of mustard, not acid shades).
However, I'm not completely sold as being an autumn also rules out navy and grey, pretty much, but steers you towards a lot of beiges and tans (think J-Lo outfits), and I think I look good in navy but really washed out in tan. The idea of never wearing grey again also fills me with horror. So, in total - I'll take stuff away from it but it won't rule my life!