  We present the results of a comparative study of the rest-frame optical and
rest-frame ultraviolet morphological properties of 117 star-forming galaxies
(SFGs), including BX, BzK, and Lyman break galaxies with B<24.5, and 15 passive
galaxies in the region covered by the Wide Field Camera 3 Early Release Science
program. Using the internal color dispersion (ICD) diagnostic, we find that the
morphological differences between the rest-frame optical and rest-frame UV
light distributions in 1.4<z<2.9 SFGs are typically small (ICD~0.02). However,
the majority are non-zero (56% at >3 sigma) and larger than we find in passive
galaxies at 1.4<z<2, for which the weighted mean ICD is 0.013. The lack of
morphological variation between individual rest-frame ultraviolet bandpasses in
z~3.2 galaxies argues against large ICDs being caused by non-uniform dust
distributions. Furthermore, the absence of a correlation between ICD and galaxy
UV-optical color suggests that the non-zero ICDs in SFGs are produced by
spatially distinct stellar populations with different ages. The SFGs with the
largest ICDs (>~0.05) generally have complex morphologies that are both
extended and asymmetric, suggesting that they are mergers-in-progress or very
large galaxies in the act of formation. We also find a correlation between
half-light radius and internal color dispersion, a fact that is not reflected
by the difference in half-light radii between bandpasses. In general, we find
that it is better to use diagnostics like the ICD to measure the morphological
properties of the difference image than it is to measure the difference in
morphological properties between bandpasses.
