Photometric selection of MPs in the HST dataset. Top panels: (m_F814W, m_F275W − m_F814W) and (m_F814W, C_{F275W, F336W, F438W}) CMDs of NGC 3201. Data are from Nardiello et al. (2018). The red and blue lines in each panel represent the two fiducial lines at the edge of the RGB used to obtain the veriticalized color and pseudo-color distribution (Δ_{F275W, F814W} and Δ_{F275W, F336W, F438W}). Bottom panel: derived chromosome map. The upper and side panels show the histogram of (Δ_{F275W, F814W} and Δ_{F275W, F336W, F438W}), respectively. Stars are colored in blue or red according to their classification as FP or SP stars, resulting from the Gaussian mixture model fit. Stars are marked with probability dependent marker sizes: the higher is the probability that a star belong to the assigned population, the larger the marker size.