F200W image of I Zw 18 with the positions of three bona fide stellar populations being overplotted and selected in the CMD using PARSEC-COLIBRI isochrones. A population of upper MS stars younger than 30 Myr (blue circles, left panel), AGB stars of intermediate ages between 0.1 and 1 Gyr (green circles, middle panel), and a population of RGB and low-mass AGB stars older than 1 Gyr (red circles, right panel). The insert panels on the bottom-left show the respected position in the CMD of the selected bona fide stellar populations.