Where to buy betty hair dye
Things You'll Need
Applicator bottle with measuring increments on the side
Obtain a hair level ring at any beauty supply store. Place the hair level ring (with the 10 different levels of hair color) against the darkest hair on your head to find your current hair color.
Find the hair color that you want to dye your hair to, using the level ring. For best results, do not go beyond three shades of your current hair level in either direction.
Determine which tones your want to add to your base color, using the level ring. If you have cool hair, which has green and blue bases, then choose colors with red and gold bases--in other words, choose colors with titles that include "warm," "golden" or "red." If you have warm hair, which is red and violet, then choose colors that have an ash (green) or blue base--neutral, ash or cool colors. If you are unsure of what base color your hair has, ask any professional at a beauty supply store and they can easily tell you. Taking your base color into consideration, choose your desired hair color with the same level that you chose in Step 2.
Count the levels between your current color and your desired color; for instance, if you have a level 3 hair color (dark brown), and you want a level 6 (dark blond), there are three levels of difference between the hair, so you should use a 30 level developer. If there are only one or two levels of difference between the original and the desired color, then use the 20 level developer. The 20 and 30 level developers are only used if you are
trying to make your hair lighter. If you want to darken your hair, use the 10 level developer.
Put gloves on both hands.
The hair dye bottle that you chose will say how many ounces of dye are in that bottle; you should use equal amounts of developer and hair dye. Pour the developer into the application bottle, making sure that you pour the same number of ounces as the hair dye bottle has, then pour the hair dye into the application bottle.
Shake until the developer and the hair dye are completely mixed together.
Section your hair into four equal parts. Dye your hair one section at a time, making sure to run the tip of the applicator bottle straight back (away from the crown of your head to the base of your neck) through the portion of sectioned-off hair. Try to make less than 1-inch rows down the roots of your hair until the whole section has dye on the roots.
After the roots are fully covered in dye in one section, move on to the next section until all of the sections have dye on the roots of the hair.
Either squirt dye onto the rest of the hair, or pour a small amount of dye on your hands (about a quarter size) and then rub the dye through your hair. Repeat this process until your hair is completely saturated with dye from roots to tips.
Leave the mixture on your hair for 25 to 30 minutes, then rinse it with warm water. Do not shampoo after rinsing, but do apply conditioner.
For best results, do not wash your hair for 24 hours after dyeing.Source: ehow.com