Relation between the OER and ΔI_sG for the 14 EBs in our sample. Different symbols and colors denote different filters, namely r, g, c, and o, following the key at the top right of the plot. The dashed line represents a least-squares fit to the data for all filters combined. The coefficient of determination is r² = 0.831, and the resulting fit is given by OER = −2.659 ΔI_sG + 1.0.