V − J color gradient vs relative size variation in four stellar mass bins. The two rows show the same data but color-coded respectively with the Sérsic index at 1.5 μm (top row) and the logarithm difference of Sérsic indices at rest-frame 1.5 μm and 0.5 μm (lower row). Just star-forming galaxies are shown. Diamonds show sub-mm-selected galaxies and are color-coded following the same color scheme of the other galaxies. Colored green lines show the running median in redshift bins. In the top right corner, we present the median uncertainties. Massive star-forming galaxies have systematically stronger size variation with wavelength and stronger color gradients than low-mass galaxies. The variation of the Sérsic index with wavelength correlates more strongly with the color gradient than with the size gradient.