While permanent color is just that — permanent — it does tend to eventually fade with time. Hello, oxymoron. However, it's the only type product that can actually lift pre-existing color out of the hair, since it relies on hydrogen peroxide and ammonia to get the job done. It's also the only type of hair color that can cover gray completely, and it also has the ability to change the hair up to four levels — sometimes even five.
After combining the tint of choice with a developer, the permanent hair dye is applied, and the ammonia immediately begins opening up the cuticle. Then, the peroxide moves in, breaking up the melanin in your hair shaft, replacing what's left with the pigment of your choice (hopefully). Might I suggest getting permanent color done at a salon, as they are trained to deal with the subtle nuances of tones, levels, and proper formulations?
The downside to permanent color is that roots will become more obvious, and the only way to remove the artificial pigments is to strip them out. To keep permanent color looking fresh, a touchup on regrowth is needed every four to eight weeks. Allow at least two weeks before other chemical services to give hair a little break, and deep condition regularly to make color last longer and keep hair healthy.