  We examine the robustness of the color-color selection of quiescent galaxies
(QGs) against contamination of dusty star-forming galaxies using the latest
submillimeter data. We selected 18,304 QG candidates out to $z\sim$ 3 using the
commonly adopted $NUV-r-J$ selection based on the high-quality multi-wavelength
COSMOS2015 catalog. Using extremely deep 450 and 850 $\mu$m catalogs from the
latest JCMT SCUBA-2 Large Programs, S2COSMOS, and STUDIES, as well as ALMA
submillimeter, VLA 3 GHz, and $Spitzer$ MIPS 24 $\mu$m catalogs, we identified
luminous dusty star-forming galaxies among the QG candidates. We also conducted
stacking analyses in the SCUBA-2 450 and 850 $\mu$m images to look for
less-luminous dusty galaxies among the QG candidates. By cross-matching to the
24 $\mu$m and 3 GHz data, we were able to identify a sub-group of
"IR-radio-bright" QGs who possess a strong 450 and 850 $\mu$m stacking signal.
The potential contamination of these luminous and less-luminous dusty galaxies
accounts for approximately 10% of the color-selected QG candidates. In
addition, there exists a spatial correlation between the luminous star-forming
galaxies and the QGs at a $\lesssim60$ kpc scale. Finally, we found a high QG
fraction among radio AGNs at $z<$ 1.5. Our data show a strong correlation
between QGs and radio AGNs, which may suggest a connection between the
quenching process and the radio-mode AGN feedback.
