Powders of the solid solutions In1-xCrxPO4 (0 <= x <= 1), In1-xCrx(PO3)(3) (0 <= x <= 1), (In1-xCrx)(4)(P2O7)(3) (0 <= x <= 0.7), and In1-xMnx(PO3)(3) (0 <= x <= 0.8) have been synthesized by solid-state reactions. Depending on the dopant concentration, these materials show striking variations in color [In1-xCrxPO4, light pink to green-brown; (In1-xCrx)(4)(P2O7)(3), light pink to red-brown; In1-xCrx(PO3)(3), pale green to green; In1-xMnx(PO3)(3), light blue to purple). Powder reflectance spectra of the solid solutions were measured in the UV/vis/NIR region (5500-35000 cm(-1)). Observed d-d electronic transition energies and results of calculations within the framework of the angular overlap model (AOM) for the low-symmetry chromophores [(MO6)-O-III] (M = Cr, Mn) are in good agreement. In the case of the mixed In/Cr phosphates, the observed color changes can be related to second-sphere ligand-field effects. Clear evidence for differences in the pi-bonding of oxygen toward Cr3+ (d(3) ion) and In3+ (d(10) ion) are observed. For In1-xMnx(PO3)(3), the variation in color is attributed to a slightly increasing elongation of the [(MnO6)-O-III] chromophore with increasing dopant concentration.