Top: residuals from the Keplerian fit in Dataset A as a function of orbital phase. Vertical dashed lines show the times of mid-transit, first, and fourth contacts. The colors of the plotted circles indicate the orbital phases of each observation. Middle: color ratio as a function of orbital phase. There is a clear correlation with the RV residuals. The decrease in the color ratio at the end of the sequence is mainly due to the increase in the airmass. Bottom: linear relation between the residuals of the Keplerian fit and the color ratio. The fit is performed on the measurements outside of the transit (filled circles); those in the transit (empty circles) roughly follow the same trend.