Release agent (stamping)
A powder or liquid applied before stamping so the mats lift cleanly off the concrete. Powder versions double as an antiquing color that lodges in the texture.
What does release agent (stamping) mean?
Powdered release is usually a contrasting color that settles into the low points of the stamped pattern, creating the depth and variation that makes stamped concrete read as stone. Liquid release leaves no color and is used where a monotone finish is wanted or where dust control matters. Excess release must be washed off before sealing, and washing too aggressively removes the antiquing effect the client is paying for.
In practice
That secondary accent color in the grout lines of a stamped patio is powdered release, and how much survives the wash determines the final look.