(B − V) vs. (V − R) plots −left column − and (V − R) vs. (R − I) plots −right column − including the reddening line. Solar colors are indicated with the ⊙ symbol. Top panels: Plutinos and other resonants. Almost all non-Plutino resonants seem to lie on the reddening line in (B − V) vs. (V − R), but their stronger correlation value is within the error-bars of the correlations for other families. Middle panels: classical KBOs and all other KBOs, except Haumea family and retrogrades. In contrast to all other families, CKBOs do not exhibit a (B − V) vs. (V − R) correlation. The existence of many CKBOs far below the reddening line (in BVR), which indicates the presence of many concave visible spectra, suggests that they may exhibit absorption features in the visible that only detailed spectroscopic studies could verify. Bottom panels: binary or multiple KBOs.