CMD of F and 1O LMC Cepheids. The boundaries of our empirical IS are shown as red circles. Fits for the upper and lower part of the red and blue edges are shown as black solid lines. Periods for these stars are shown with a color gradient. For 1O Cepheids, periods were fundamentalized. Dashed lines of constant periods are overplotted. In most cases, error bars are smaller than the size of the points.