Abstract: A method of treating blue or black denim fabric to change its color, a composition used to create the color change, and the denim fabric produced thereby. The composition is applied to the denim fabric in a washing machine and comprises cellulase enzyme, a detergent, a salt, a buffer and dyestuffs. The fabric is either stonewashed before or during application of the composition. After the composition is applied, the resulting denim fabric is stonewashed in appearance and has a surface displaying two sets of light and dark areas of different shades of the same color.