OGLE passbands amplitude ratios. Top: $\frac{Ampl(I)}{Ampl(V)}$ ratios for the RRLs of the bulge. The red circles (triangles) display the RRc (RRab) that passed a recursive sigma clipping (cut at 2σ) for the linear fit. The black solid lines display the linear fits of the two samples. The black dashed lines display the standard deviation of the linear fit. Middle: Same as top but for the LMC sample. In this case, the fit is a constant. Bottom: Same as middle but for the SMC sample.