Fig. 2. Reflectance spectra of chromatic (color) and achromatic (grey) papers used in the present experiments. The spectra are shown relative to the maximal reflectance in a set of the training color and the corresponding four different greys. (A) Blue and four corresponding grey papers: with the same subjective brightness (Gr-B-s), and the same quantum catch for the blue (Gr-B-b), green (Gr-B-g) and red (Gr-B-r) receptors. (B) Green and four corresponding grey papers. (C) Red and four corresponding grey papers. For the calculated number of quantum catch, see Table 1.