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 .