Kepler-418b transit observed by the GTC in Sloan g′ and z′ filters. Upper panel: observed light curves and the 95% confidence limits for the transit models, lower panel: color differences for the observed and modeled data in units of normalized flux, with the zero-point fitted to the off-transit data. The dashed vertical line represents the expected beginning of the transit, and the solid black line shows the fitted transit center. The 95% confidence limits for each value are depicted as gray shaded ares, but these fall inside the line widths.