Examples of asteroid classes (A, D, S, and V) that are degenerate over the visible wavelength range. For reference, the wavelength coverage of each photometric filter and grism on board Euclid is shown, together with the filter sets of SDSS and LSST (u, g, r, i, z; Ivezić et al. 2001), VISTA and UKIDSS (Y, J, H, Ks; Hewett et al. 2006), and the Gaia blue and red photometers (BP, RP) that will produce low-resolution spectra (resolving power of a few tens; Delbo et al. 2012).