Similarity Φ values of the alteration model to the ratio of the respective pairs of asteroid-meteorite reflectance spectra. Darker colours indicate greater similarity. Red colours show that the asteroid is reddened with respect to the meteorite, and blue colours indicate blueing. Pairs that exceed the similarity levels S_j have the respective j superimposed. Black dotted lines separate different classes of asteroids and meteorites. Asteroids are labelled by their number, while Barbarian asteroids are marked with green labels.