  Context.Spatially-resoved cicrumstellar disk spectrum and composition can
provide valuable insights into the bulk composition of forming planets, as well
as the mineralogical signatures that emerge during and after planet formation.
Aims. We aim to systemically extract the RX~J1604.3-213010 (J1604 hereafter)
protoplanetary disk in high-contrast imaging observations, and obtain its
multi-band reflectance in visible to near-infrared wavelengths. Methods. We
obtained coronagraphic observations of J1604 from the Keck Observatory's NIRC2
instrument, and archival data from the Very Large Telescope's SPHERE
instrument. Using archival images to remove star light and speckles, we
recovered the J1604 disk and obtained its surface brightness using forward
modeling. Together with polarization data, we obtained the relative reflectance
of the disk in $R$, $J$, $H$ ($H2$ and $H3$), $K$ ($K1$ and $K2$), and $L'$
bands spanning two years. Results. Relative to the J1604 star, the resolved
disk has a reflectance of ${\sim}10^{-1}$~arcsec$^{-2}$ in $R$ through $H$
bands and ${\sim}10^{-2}$~arcsec$^{-2}$ in $K$ and $L'$ bands, showing a blue
color. Together with other systems, we summarized the multi-band reflectance
for 9 systems. We also identified varying disk geometry structure, and a shadow
that vanished between June and August in 2015. Conclusions. Motivated by
broad-band observations, the deployment of cutting-edge technologies could
yield higher-resolution reflection spectra, thereby informing the dust
composition of disks in scattered light in the future. With multi-epoch
observations, variable shadows have the potential to deepen insights into the
dynamic characteristics of inner disk regions.
