We propose a planar, ultrathin, subwavelength spectral light separator that enables efficient, angularly robust, spatially coregistered decomposition of light into its spectral components. The device consists of a collection of spectrally tuned “meta-atoms” and achieves spectral selectivity by utilizing strong localized resonance supported by each individual meta-atom. The three-dimensional meta-atoms are formed by resonant subwavelength-size rectangular apertures in a planar metallic film of deep-subwavelength thickness. The overall physical cross-sectional area of the device is subwavelength, and its thickness is deep-subwavelength. Different spectral components of light are simultaneously separated and collected in different subwavelength-size aperture pairs, where each aperture pair is composed of two perpendicularly oriented, same-size apertures; and different aperture pairs collect their light from overlapping cross-sectional regions. Hence, spatial coregistration errors between different spectral c...