Imo it has made a huge difference, but i didn not have them done, as such. Figured it out from a couple of books and websites. I think the main book i used was called Color (American boook) Me Confident, and the website by Lora Alexander. Sorry I cant provide link as I am posting from an e reader.
For me it has really helped but I really didnt have a clue before, my wardrobe was full of loads of different colours. I went to Colour Me Beautiful, it is slightly cringey while you are doing the consultation as it is hard not to think "WTF am I doing here talking about being a Winter Sprinter or whatever" but the lady was lovely and although it hasnt changed my life yet, it really helps when shopping as you go straight to the colours you know suit you and you look good in. I couldnt have figured it out from the books but lots of others have. I suppose you could start by getting book from library and see if that works for you.
I just bought a Trinny and Susannah book - What you Wear Can Change Your Life. It has a large section on colours - what suits your skin tone, but more than that - it takes every single colour you can think of and matches it to all the other colours that work with it. I thought it was incredibly helpful. I was able to work out the colours that suit my skin tone and it's transformed my wardrobe. Would recommend - and it's probably a lot cheaper than Colour me Beautiful.
rubyrubyruby - I do think that particular book is well worth it just for the colour section. T&S get a load of flack but they aren't body or designer fascists and a lot of what they say makes sense. To me anyway.