  Most comets are volatile-rich bodies that have recently entered the inner
solar system following long-term storage in the Kuiper belt and the Oort cloud
reservoirs. These reservoirs feed several distinct, short-lived "small body"
populations. Here, we present new measurements of the optical colors of
cometary and comet-related bodies including long-period (Oort cloud) comets,
Damocloids (probable inactive nuclei of long-period comets) and Centaurs
(recent escapees from the Kuiper belt and precursors to the Jupiter family
comets). We combine the new measurements with published data on short-period
comets, Jovian Trojans and Kuiper belt objects to examine the color systematics
of the comet-related populations. We find that the mean optical colors of the
dust in short-period and long-period comets are identical within the
uncertainties of measurement, as are the colors of the dust and of the
underlying nuclei. These populations show no evidence for scattering by
optically-small particles or for compositional gradients, even at the largest
distances from the Sun, and no evidence for ultrared matter. Consistent with
earlier work, ultrared surfaces are common in the Kuiper belt and on the
Centaurs, but not in other small body populations, suggesting that this
material is hidden or destroyed upon entry to the inner solar system. The onset
of activity in the Centaurs and the disappearance of the ultrared matter in
this population begin at about the same perihelion distance ($\sim$10 AU),
suggesting that the two are related. Blanketing of primordial surface materials
by the fallback of sub-orbital ejecta, for which we calculate a very short
timescale, is the likely mechanism. The same process should operate on any
mass-losing body, explaining the absence of ultrared surface material in the
entire comet population.
