Color distribution of the noise in the Control Field and the resulting color distribution by adding an artificial constant color structure. Upper left panels: color vs. surface brightness values (red dots) of pixels dominated by the noise. Their color distribution is very well fitted by a Lorentzian function (red curve) as shown in the right side of the plot. Upper right panel: same but adding a constant color structure (blue dots) fitted by a Gaussian function (blue curve). The purple curve is the result of combining a Lorentzian plus a Gaussian function. The horizontal dashed lines correspond to the calculated centers of the Lorentzian and Gaussian functions. Bottom panels: correlation between the flux of the different bands. The dotted line corresponds to the best fit using a linear least-squares approximation in one-dimension.