Best-fit de-reddened and reddened SEDs with 1σ errors for SMSS J2157 (purple and pink lines, respectively), as derived in Sect. 3.2. The 1 keV luminosity is shown as a left-pointing coral red triangle; REM/ROS2 g, r, i, z data are represented by orange circles; Y, J, and Ks points from VISTA are shown as down-pointing green triangles; the H point from 2MASS is represented by a down-pointing blue triangle; and golden yellow squares represent the W1-W4 WISE channels. The uncertainties of data points are shown but are smaller than the symbol size.