Single Hair Process vs. Double Hair Process. What's the difference?
A single process refers to any color service that is done in one step. It can also be reffered to as a base color or a "root touch up", but it is not restricted to coloring just on the "roots". This is generally a permanent color that is applied either jus to the roots or all over from roots to ends. a single process can also be a demi-permanent color or a glaze, which is a type of color that only deposits color into the hair.
A single process can cover up your grays, blended your grays for a more a natural look that gradually washes out, or creates more richness, changes tone and adds shine.
A double process color refers to a two-step service. This is generally done by either lightening the hair first, then going in after and applying a color or glaze, OR this is done by applying a color then following up again with a color (permanent, demi, or semi).
A double process is great for those who want that Disneys Princess Elsa hair color or the talented Gwen Stefani bright platinum blonde. This technique of coloring is also good for someone who is going from a really bright color to a darker one, to help it last long and achieve the desired look.