A method has been developed to improve the stability of a color measurement system that measures reflectances using matrix-transformation method. The transformation matrix can be obtained by training with a raw measurement matrix and a master reflectance matrix. The raw measurement matrix can be stacked with one or more of its variations, with each variation being some random noise added onto a part or the whole original raw signal matrix. The same number of master reflectance matrices are also stacked to match the size and sample ordering of the raw measurement matrix. The resulting transformation matrix will be more stable and less sensitive to the measurement noise.