0.4–6 keV count rate vs. (a) V-band magnitude and (b) hardness ratio for the GC-LMXBs. The hardness ratio is defined as HR = ( H2 − M − S1)/( H2 + M + S1). Blue and red GCs are plotted with blue triangles and red open circles, respectively. The UCD is plotted with a filled circle for comparison. The horizontal dashed line in panel (a) represents the Eddington luminosity of an accreting NS with a mass of 1.4  M _☉. The vertical dashed lines in panel (b), from left to right, correspond to hardness ratios for an absorbed power-law spectrum with a fixed N _H = 10 ²¹ cm ⁻² and a photon index of 2.0, 1.7, and 1.4, respectively.