I worked at Sally Beauty Supply for a little over a year - and about a year ago. I saw every kind of disaster possible when it comes to someone coloring their own hair. Here's some food for thought.
1.) You have to have good luck if you want to color your own hair.
2.) I swear by having someone who knows their stuff, do the coloring. The person I go to is terrific.
3.) If you elect to do your own, stick with one manufacturing line, don't keep changing them. You will never get the same color again if you do. Many people buy their products at the grocery store or Walmart and don't remember or care to remember what they bought the last time. You can go to Sally's and buy exactly the same product the hair salons use. You have to know how to mix the color (instructions are included) and you have to know what to buy.
4.) Places like Sally's don't require their sales people to be hairdressers. I know. They can usually help you correct your errors but will be hard pressed to suggest what is good for you and the color you want. Back to the hair salon with you.
5.) If you do have enough nerve to ask you salon person for the colors and numbers of your color (assuming you like what he/she has been using on you) then you can buy the color at a place like Sally's and do it yourself. Oh and just do the roots after the first color, not the entire head each time!
6.) My salon person uses a glaze on my hair and lets the gray pickup some color and it actually looks like my hair is highlighted. When she first colors it, I am not wild about it but within a couple of washings, I like it and it lasts for 8 weeks. Then back to her. I don't have my hair cut all that often and it would be cheaper if I didn't have her blow it out and style it. It is my only true splurge in life.
7.) You can remove any color you put in your hair by mistake. BUT you are left with no color (icky yellowish grayish awful color) and then must wait a day or so until you try again.
8.) I recommend going to a good salon if you want to look professional and or have a hair color that stands out in a positive way.
Hair can really make or break a person's appearance. I had stopped coloring my hair for several years and I just wasn't happy with how old it made me look, so I went back and agreed to do the glazing thing rather than a solid color. My hair looks very natural and I love it!