  We propose a chemical and dynamical process to explain the surface colors of
the Kuiper belt. In our hypothesis, the initial bulk compositions of the bodies
themselves can be quite diverse -- as is seen in comets -- but the early
surface compositions are set by volatile evaporation after the objects are
formed. Strong gradients in surface composition, coupled with UV and particle
irradiation, lead to the surface colors that are seen today. The objects formed
in the inner part of the primordial belt retain only H2O and CO2 as the major
ice species on their surfaces. Irradiation of these species plausibly results
in the dark neutrally colored centaurs and KBOs. Object formed further in the
disk retain CH3OH, which has been shown to lead to brighter redder surfaces
after irradiation, as seen in the brighter redder centaurs and KBOs. Objects
formed at the current location of the cold classical Kuiper belt uniquely
retain NH3, which has been shown to affect irradiation chemistry and could
plausibly lead to the unique colors of these objects. We propose observational
and experimental tests of this hypothesis.
