Distributions of GCs on the plane between the derived binary fraction f_der(q > 0.5) and the EW/MAG of spectral absorption feature index (in Å or mag), which is obtained at the resolution of FWHM_Lick/IDS. In each panel, each GC in the new sample is connected by a line, blue, green, and black symbols correspond to the equivalent radius in the U17, S05-1, and S05-2 observations, respectively. The name of each GC is given to the right of the corresponding symbol. The remaining GCs in the original sample are given in grey points. The dotted lines in the background have the same spectral absorption feature index versus the binary-fraction slope as for NGC 6121.