The major difference is how long you want the color to last and how much of a change you actually want. If you're looking for something subtle, such as adding a layer of color or deepening your own natural hair color, a semi-permanent color is the best option for you.

Semi-permanent colors are designed to wash out after about 6 to 12 shampoos. The real benefit to them is that the color is temporary, so there is not a big change "commitment” on your part. And, just think, you won’t have to deal with those pesky noticeable roots.

One thing to note is that semi-permanents actually darken the hair. They don’t contain any ammonia or peroxide, so they can’t ever lighten your hair. So keep in mind that if you're looking to go dramatically lighter, semi-permanents are not the best choice for you.

If you want a longer-lasting option, consider something called demi-permanent color. This lasts about twice as long as semi-permanent dye and has the same basic properties as semi-permanent color.

But, if you want that dramatic change, a permanent hair color is your best option. What do we mean by dramatic? Any time that you “lighten” your hair or make it more than a shade or two darker, that's dramatic. If you are looking to hide the grays, permanent color is the only way to go.

Permanent color does not wash out with shampooing. It is a blend of peroxide and ammonia that actually removes the color pigment from your hair and then deposits new color on top. When your hair grows in, the original color appears in the form of roots. And you will have to “re-touch” the roots every six weeks or so (depending on how fast your hair grows).

A single process is just the application of one color (or toner) to achieve an all-over color. You can still have some contrast depending on the color used or your existing hair color, but there is only one application - hence the term “single process.”

Foils are used to introduce multiple colors to a client’s hair. The foils allow the stylist to place color strategically in a hair design to achieve a certain look. Foils are also utilized when a stylist is trying to “highlight” the hair. Foils are not usually used on very short hair.