(﹩\mathrm{FUV}\,-V﹩) color limits of sources detected in far‐UV frames but not in optical frames for fields 1, 2, and 3. The upper limit in color for each source is plotted with a vertical bar. The upper limits to the V magnitudes are determined using the fluxes plus 3 σ when the measured fluxes are positive and 3 σ when the measured fluxes are negative. The bluest color permitted for an old population dominated in the UV by EHB stars is ﹩( \mathrm{FUV}\,-V) _{0}\sim 0.1﹩ (see text).