The excess in UV color (GALEX/NUV–SDSS∕r, blue shading) of binary systems containing a stripped star compared to the UV color of the main sequence companion only. A detectable UV excess could be ≳0.05 mag depending on the instrument. We show binary system combinations covering wide mass ranges of stripped stars and companion stars. The stripped star dominates the optical emission in systems with low-mass companions and massive stripped stars (gray hatched region). The example systems of Fig. 7 are marked with black squares and labelledwith corresponding panel letter. The few binaries containing B-type stars and detected stripped stars are marked and labelled in black.