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Abstract In this study, we extend the dust-independent Hatzidimitriou relation between cluster age andd_B−Rcolor difference between the red giant branch (RGB) and red clump to younger cluster ages. We perform membership analysis on 14 galactic open clusters using Gaia DR3 astrometry, then compute the difference in color of the RGB and red clumpd_B−Rusing Gaia photometry. We also computed_B−Rfor five fields surrounding Small Magellanic Cloud clusters. We find that the trend derived from older clusters does not extrapolate to younger ages and becomes double valued. We confirm thatd_B−Ris independent of metallicity. Current stellar evolutionary isochrones do not quantitatively reproduce the trend and furthermore predict an increased color gap with a decrease in metallicity that is not echoed in the data. Integrated light models based on current isochrones exaggerate the color change over the ​​​​​​−0.5 < [Fe/H] < 0 interval at the few-percent level.