Color–color diagrams for stellar templates (open circles) and sources identified as stars (black triangles and blue squares) in the GROND sample. Offsets of + 0.2, + 0.08, + 0.08, and + 0.1 mag to the g′, r′, i′, and z′ zeropoints are applied, except in the case of direct SDSS calibration. The sources represented by black triangles are SDSS calibrated, while the blue squares represent a zeropoint calibration.