COLOR IMAGE ERROR IN SPECAL NOISE REDUCTION

I am trying to run the specal noise reduction code. It is working completely fine with the balck and white specal noise image but when I run the code with a color specal noise image it is showing the following error. I feel it is due to the matrix dimension mismatch while calculating the y. Reason may be balck white image of a*a dimension but where as color image is of a*a*b dimension. Kindly share your suggestion to resolve this, It would be really a great help. I am attaching the reference image below.