Magnetic starspot filling fractions as a function of the rotational Rossby number parameter for stars in our study sample. Stars are colored and assigned a marker according to their host cluster. For comparison, the light blue swathe represents the fitted relation found by L. Cao & M. H. Pinsonneault (2022) in their study of the Pleiades, which appears to trace the lower envelope of the spot–Rossby relation for our larger sample of open clusters with ages spanning 10–670 Myr.