Color–color/magnitude diagrams for the companion COCONUTS-1B (red). We use gray squares to show known field M6–T9 dwarfs from Best et al. (2018) and W.M.J. Best et al. (2020, in preparation), which have infrared absolute magnitudes with S/N > 5 and are not young, binaries, or subdwarfs. We use black squares and black error bars to show the typical photometry and 1σ confidence limits of these field dwarfs in each spectral type bin. The y_P1 and J_MKO absolute magnitudes of COCONUTS-1B are computed by assuming its primary star’s Gaia DR2 parallax. The companion’s colors and magnitudes both suggest a mid-T dwarf located at the distance of the white dwarf primary.