We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relate to the formation of galaxies at $1.5 < z < 3.5$. We use the Internal Color Dispersion
(ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with S{e}rsic indexes $< 2$) and stellar masses between $10 < mathrm{Log~M/ M_odot}< 11$. There is a marked decrease in the ICD as the stellar mass and/or the Sersic index increases. By studying the relations between the ICD and other galaxy properties including sizes, total colors, star-formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, $10 < mathrm{Log~M/ M_odot} < 11$, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses, and/or higher S{e}rsic index ($n > 2$) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have both a quiescent bulge along with a star forming disk, typical of Hubble Sequence galaxies, this is most common for stellar masses $10 < mathrm{Log~M/M_odot} < 11$ and when the bulge component remains relatively small ($n<2$).
