a) Detection fraction for the NIBLES Nançay sample (gray) and the Arecibo follow-up sample (black) as a function of g−i color. b) Detection fractions as a function of r-band luminosity. Error bars for the Nançay data are the standard deviation of the binomial distribution and the error bars for the Arecibo data were calculated following Gehrels (1986) using the 90% confidence intervals. Bin sizes are 0.3 for a) and 1 for b).