I've been coloring my own hair using store-bought hair dye for years and years. I've known women who try this for the first time, see the color when they're done, and run to the salon and pay a lot of money for them to "fix" it.
Well, in case you've never colored your own hair and you've ever thought of trying it, let me let you in on a handy little piece of knowledge:
The color your hair comes out immediately after coloring it IS NOT THE COLOR IT'S REALLY GOING TO BE 3-5 SHAMPOOS LATER. You have to give it a couple of days and a few washings - quite a bit of color comes out initially, and THEN you will see the true color your hair has become.
For example, I just did my hair a color called something to the effect of "Medium Reddish Brown". It looked more like "Hideous Way Too Red, Or Shall I Call It Orange, and Not Really Very Brown" for the first two days. However, now it has transformed into the medium reddish brown as promised on the box, and it's very nice - I've gotten two compliments on it already.
In my opinion, coloring your hair at home is easy and VERY INEXPENSIVE. And you can nearly always get a coupon too. The trade-off is you may have wonky colored hair the first day or two or three. (Although I suppose you could just wash your hair a few times the first day to speed up the process.)
Anyway, if you've never done it and and you want to try it and your hair comes out too dark / too red / too light - just chill. Wash your hair a few times. It will probably be ok!