PersulfatesBleaches-Color removers such as Matrix Color Erase, L'Oreal Effasol, ../forum_posts.asp?TID=58626# - Dye-solvents since they can be mixed with warm water or various volumes of peroxide to customize the amount of lift needed - there is absolutely no danger or worry of the color re-developing or darkening. The drawbacks are, they do damage the hair in the same way as a bleach, create hair weakening Cysteic Acid, and can leave the hair with excessive porosity.
On over-lightened, over-permed, relaxed or super-damaged hair, a Dye-solvent for color removal is more appropriate since it is non-damaging. In some cases, a persulfate-based color remover can be faster than a dye-solvent since you are removing the artifical pigment AND lightening the natural pigment at the same time.
Sulfonated Castor Oils-The final type of color remover is Clairol's Metalex - I believe it is the only product of its kind, at least I'm not aware of another. Metalex is based on Sulfonated Castor Oil and is used to remove Henna, Metallic Salts, Color Restorer's and any type of temporary/semi-permanent color that coats the hair, such as Cellophanes, Prizms, Jazzing, Loving Care, ../forum_posts.asp?TID=58626# - Metalex also reconditions hair damaged by over-tinting or lightening - if rinsed from the hair and not shampooed out, it stops breakage. It will also soften the curl of a new perm without relaxing it. Metalex won't affect permanent tints or toners, but if a permanent color goes a little bit too dark, Metalex can be applied to lift the shade slightly - but only when applied right after tinting. It causes absolutely no damage to the hair.
For lifting dark colors like Loving Care, Metalex is mixed with 20 Volume peroxide and 'cooked' under a warm dryer for 30 minutes. For lighter colors and coatings, Metalex without peroxide is used. You can also mix Metalex with shampoo to create a build-up removal shampoo. After rinsing Metalex from the hair, give a light shampoo. If there is breakage, just rinse the Metalex out without a shampoo. You can also use Metalex as a general reconditioning treatment or before a perm, bleach or color. The oils in it are very good at restoring shine and spring to over-bleached hair and gives it a healthy glow. For permanent colors that also contain Direct Dye's, use Metalex first to lift the direct dyes and recondition at the same time. Then you can use either bleach or a dye-solvent to remove the remaining oxidative pigment.
Metalex by Clairol is another one of those indespensable products that no salon should be without - it's an old product but a good one.
One other product that, technically is a color remover but not classified with the above, is good old powder bleach – most manufacturers give specific instructions on how to mix their powder bleach to create a color remover, but in most cases it’s a pump of shampoo with one or two scoops of powder bleach and an equal amount of 10 or 20 volume peroxide.
Powder bleaches can be mixed with warm or hot water too for more gentle removal, and are usually much cheaper than persulfate-based color removers, since you buy them by the bucket instead of by the packet. Another plus is you probably always have a powder bleach on hand!"

Hope this is helpful to people!