Whether you use a boxed hair color at home or you get it done professionally at a salon, the recommended wait time before washing your hair is 24 hours. If you use a double-process color (such as a base color and highlights), try to go 48 hours without washing your hair to allow your hair and scalp to build up their natural oils again.
If you have unexpected results such as an overly vibrant, dark or ashy color, the professionals at Schwarzkopf (a leader in the hair color industry) suggest washing your hair immediately.
Wait a minimum of 24 hours after any color process for best results, unless you want to tone down the color-in, in which case wash it immediately. Always follow up with a deep conditioner to restore moisture to the hair.