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We measure starspot filling fractions for 240 stars in the Pleiades and M67open star clusters using APOGEE high-resolution H-band spectra. For this workwe developed a modified spectroscopic pipeline which solves for starspotfilling fraction and starspot temperature contrast. We exclude binary stars,finding that the large majority of binaries in these clusters (80%) can beidentified from Gaia DR3 and APOGEE criteria -- important for field starapplications. Our data agree well with independent activity proxies, indicatingthat this technique recovers real starspot signals. In the Pleiades, fillingfractions saturate at a mean level of 0.248$\pm$0.005 for active stars with adecline at slower rotation; we present fitting functions as a function ofRossby number. In M67, we recover low mean filling fractions of 0.030$\pm$0.008and 0.003$\pm$0.002 for main sequence GK stars and evolved red giantsrespectively, confirming that the technique does not produce spurious spotsignals in inactive stars. Starspots also modify the derived spectroscopiceffective temperatures and convective overturn timescales. Effectivetemperatures for active stars are offset from inactive ones by -109$\pm$11 K,in agreement with the Pecaut & Mamajek empirical scale. Starspot fillingfractions at the level measured in active stars changes their inferred overturntimescale, which biases the derived threshold for saturation. Finally, weidentify a population of stars statistically discrepant from meanactivity-Rossby relations and present evidence that these are genuinedepartures from a Rossby scaling. Our technique is applicable to the fullAPOGEE catalog, with broad applications to stellar, galactic, and exoplanetaryastrophysics.

Starspots and Magnetism: Testing the Activity Paradigm in the Pleiades and M67