Are the chemicals used in salon hair coloring much different than store bought? If so, what is the difference?
Here is a MSDS (Material Safety Data Sheet) that I found on the site “How Stuff Works”… very good site and will give you all the info you need on the chemical end of it… http://science.howstuffworks.com/framed.htm?parent=hair-coloring.htm&url=http://www.herc.org/library/msds/wella.htm
And here it take you through a bunch of info you might want to know also http://science.howstuffworks.com/hair-coloring.htm
That said, I’ve been colouring my hair for around 18 years now… and I’ve tried both at home and salon. I can only state my opinion of the difference… and that’s the salon colourist has been trained and you haven’t. They can mix colours and give you the hair colour you want… but with the box at home you never know what your going to get. Even with the at home “strand test” the hair on the back of your head may colour differently from the hair on the top. (I can vouch for that one… hehe) The salon can also “fix it” if they happen to screw up. But then a salon will charge you alot more than the home product costs. However, I don’t know if there is a difference in chemicals or not… you can always go to the beauty products store and get the colour the salon uses yourself.
From my experience semi permanent colour works better for me because my hair grows so fast I end up doing it once a month. It tends to damage hair less and have no ammonia or peroxide… use a bit of common sense though… they say it washes out in 6 to 12 shampoos, but in my experience it doesn’t wash out completely.
Oh… and, yes, I colour my hair at home… but that’s after I found the colour I like and the technique to do it right.
Hope this helps you out. 
I don’t have my hair colored anymore, but I once asked my colorist what she used, and it was a store brand—just purchased wholesale by the salon.
I can’t believe the quick response! Thanks so much!
The products are pretty well identical - what you’re paying for in a salon is expertise.
Basically, if you want to slightly alter you hair color - about one shade (someone medium blond going medium-light or light blond) - you can probably do it at home. However, if you want to do something dramatic like a 5 shade difference, out of your natural color family, with highlights (Think someone with dark brown hair going strawberry blond with redish undertones), unless you have training or a lot of exerience you’re going to make a mess.
So - if you’re trying to perk up your color you can safely do it at home. If you’re trying to re-invent yourself, or do color correction, see a professional.