(a) Color–albedo diagram for 109 TNOs showing two main clusters, one composed of dark neutral objects (blue points, albedos ~0.05 and S′ ~ 10%), and another of bright red objects (red points, albedo ~0.15 and S′ ~ 30%). The black points have large uncertainties and ambiguous surface type. Large TNOs (green) and objects with Haumea-type surfaces (orange) occupy a third group (bottom right). Albedo/color histograms are shown in gray. (b) Smooth 2D histogram (Gaussian kernel, width 3% of full ranges, weighted by errorbars) of the color–albedo distribution shown in panel (a).