Acid stains are applied topically, unlike integral colours which are blended into the mix. Stains provide a patina look that highlight areas of the concrete, similar to how stain on wood shows the grain. Stains will not rub off as they are a reaction with the concrete. The colours that can be achieved with acid stains are similar to what you would see in nature. For example, lime green and fire engine red is not possible, but a mossy green and rusty red would be more accurate.