Your dark roots are showing, but you don't have the money to pay your stylist to touch up your color for you. Do you buy a box of color from the drugstore or simply wait until you do have the money? Only you can decide what to do. However, you should know that if you decide to color your hair at home, your technique has to be flawless, especially if you're lightening your hair. You can only put color on the root or regrowth portion of your hair. If you overlap color onto the previously colored sections, you may suffer one of the following consequences.
If you overlap the color, you can end up with a discoloration pattern that stylists call banding. Basically, the overlapped sections will be a different color than your roots or the ends of your hair, resulting in a banded appearance. You might also find it difficult to match your roots to your existing color. Stylists and colorists don't simply apply color straight out of a box. They mix several things to get your exact formula.
Overlapping color onto previously colored sections results in unnecessary hair damage. Color always causes damage, but when you color the same hair numerous times, the damage is compounded. Your hair may feel dry and brittle after you color it or it may even become over-processed, a severe type of damage that can be catastrophic for your hair.
Severely damaged and over-processed hair can't hold on to hair color. The cuticle of the hair is so damaged that it won't actually trap color pigment inside. When this occurs, you end up with faded color that you can't fix. No matter how many times you try to put the color back in, it will always fade over the course of a few days or weeks.
Over-processed hair may also break off immediately or over the course of several days. It may also melt away. Damage from hair color can be so bad that you're left with an inch or two of hair while the rest of your long locks are in the sink.
As you can see, there are several reasons why you need to get your technique just right if you decide to touch up your roots at home. If you're not confident that you can do the job correctly, wait for your stylist to do it for you.