  Near-IR photometry for 20 radio-loud z>3 quasars, 16 of which are radio-
selected, are presented. These data sample the rest-frame optical/UV continuum,
which is commonly interpreted as emission from an accretion disk. In a previous
study, we compared the rest-frame optical/UV continuum shapes of 15 optically
bright (V<17.5) z>3 quasars with those of 27 low redshift (z~0.1) ones that
were matched to the high redshift sample in evolved luminosity (i.e. having
luminosities ranging from 1-7 times the characteristic luminosity, L*, where
L*~(1+z)^{~3}) to look for signs of evolution in the central engines. We found
the continuum shapes at z~0.1 and z>3 similar, consistent with no significant
change in the ratio mdot/M, where mdot is the accretion rate with respect to
the Eddington rate and M is the black hole mass. This study expands our earlier
high redshift sample to lower luminosity, away from extreme objects and towards
a luminosity overlap with lower redshift samples. The distribution of
rest-frame optical/UV continuum shapes for this fainter sample is broader,
extending further to the red than that of the brighter z>3 one. Three quasars
from this fainter sample, two radio-selected and one optically-selected, have
optical continuum slopes alpha<-1 (F_{nu}~nu^{alpha}). The optically-selected
one, LBQS0056+0125, appears to be reddened by dust along the line of sight or
in the host galaxy, whereas the radio-selected ones, PKS2215+02 and
TXS2358+189, could derive their red continua from the contribution of a
relatively strong synchrotron component to the rest-frame optical. These
objects may represent a bridge to a population of very red high redshift
quasars to which ongoing or future near-IR, optical and deep X-ray surveys will
be sensitive.
