Four mean spectra, normalized at 0.55 μm. The spectra, from bottom to the top, are in blue, green, yellow and red and correspond to BB, BR, IR and RR taxonomical classes, respectively. The error in dashed line appear at ±1σ level, see text for more explanation on errors determination. The photometrical data (centered at 0.655, 0.795, 1.25, 1.65 and 2.165 μm) giving the average reflectance values for each taxon are taken from Perna et al. (2010).