Without color, stucco can be drab and unattractive. Stucco will take on the color of the components its made of including sand, gray or white portland cement or lime. A dry iron oxide pigment can be integrated into the stucco during the mixing process to give a deep layer of color which will keep the application consistent over time even if the building sustains any damage. Or, a stain can be applied after installation and drying is complete, this will give greater control especially if there’s a need to match the color of an existing stucco wall for example during the construction of a home expansion or adding to an existing building.
If a wall contains a waterproofing coating or polymer-modified cement, the stain will not absorb into the wall. The best path of greatest success is to apply a stain to new stucco wall, or an existing stucco wall free of any paint, stain or sealers. Start with staining a small inconspicuous area, allow it to dry and make sure the final color is what you want. You can add additional layers of stain to achieve a darker color. Use a Hudson-type sprayer to apply your stain, several lighter coats will give better results than one heavy coat. Wait one week or more and decide if you want to add more.
More info is available in The Stucco Book, The Basics by Herb Nordmeyer