  In this Letter, we analyse the radial UV-optical color distributions in a
sample of low redshift green valley (GV) galaxies, with the Galaxy Evolution
Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the
residual recent star formation distribute in these galaxies. We find that the
dust-corrected $u-r$ colors of early-type galaxies (ETGs) are flat out to
$R_{90}$, while the colors turn blue monotonously when $r>0.5R_{50}$ for
late-type galaxies (LTGs). More than a half of the ETGs are blue-cored and have
remarkable positive NUV$-r$ color gradients, suggesting that their star
formation are centrally concentrated; the rest have flat color distributions
out to $R_{90}$. The centrally concentrated star formation activity in a large
portion of ETGs is confirmed by the SDSS spectroscopy, showing that $\sim$50 %
ETGs have EW(H$\rm \alpha$)$>6.0$ \AA. For the LTGs, 95% of them show uniform
radial color profiles, which can be interpreted as a red bulge plus an extended
blue disk. The links between the two kinds of ETGs, e.g., those objects having
remarkable "blue-cored" and those having flat color gradients, are less known
and require future investigations. It is suggested that the LTGs follow a
general picture that quenching first occur in the core regions, and then
finally extend to the rest of the galaxy. Our results can be re-examined and
have important implications for the IFU surveys, such as MaNGA and SAMI.
