  One of the most enigmatic and hitherto unexplained properties of Jupiter
Trojans is their bimodal color distribution. This bimodality is indicative of
two sub-populations within the Trojans, which have distinct size distributions.
In this paper, we present a simple, plausible hypothesis for the origin and
evolution of the two Trojan color sub-populations. In the framework of
dynamical instability models of early Solar System evolution, which suggest a
common primordial progenitor population for both Trojans and Kuiper belt
objects, we use observational constraints to assert that the color bimodalities
evident in both minor body populations developed within the primordial
population prior to the onset of instability. We show that, beginning with an
initial composition of rock and ices, location-dependent volatile loss through
sublimation in this primordial population could have led to sharp changes in
the surface composition with heliocentric distance. We propose that the
depletion or retention of H$_{2}$S ice on the surface of these objects was the
key factor in creating an initial color bimodality. Objects that retained
H$_{2}$S on their surfaces developed characteristically redder colors upon
irradiation than those that did not. After the bodies from the primordial
population were scattered and emplaced into their current positions, they
preserved this primordial color bimodality to the present day. We explore
predictions of the volatile loss model - in particular, the effect of
collisions within the Trojan population on the size distributions of the two
sub-populations - and propose further experimental and observational tests of
our hypothesis
