Norvell Optimum Booth Solution - Dark / 1 Gallon - 128 oz. - 3,785 mL. Optimum solutions are designed with the Natural Color Complex. This complex is infused with natural ingredients to protect and nourish skin for just-off-the-beach-color. These tanning solutions are available as gradual tans or instant cosmetic bronzers with extended tans. Designed for early model spray tanning booths.