Intense flash‐tube irradiation produces a brownish color in CaWO4:Nd, principally by absorption of wavelengths shorter than 300 m&mgr;. Initially, the photolytic optical absorption has a peak near 3.0 eV forE∥c, and at 3.0 eV forE⊥c. At 300°K, there is a fast partial decay of the optical absorption within a few hours followed by a slow subsequent decay which stabilizes within a few days. On approach to equilibrium, the initial 3.0‐eVE∥cpeak decomposes to two peaks at 2.5 and 3.0 eV. The absorption forE⊥cdiminishes with time, but the peak remains near 3.0 eV. The absorption coefficient forE∥cin this photolytic case is always about twice that forE⊥c. The photolytic coloring is removed by heating at 300°C for a few hours. It is unaffected by compensation of Nd with Na. Reduction of lightly doped CaWO4:Nd induces an optical absorption which peaks at 2.5 eV for bothE∥candE⊥c. For heavily doped CaWO4:Nd:Na, absorption peaks at 2.2 eV forE⊥cand 2.2 and 2.9 eV forE∥care produced. Thus, reduction and photolytic coloring have fairly similar spectra. The removal of reduction coloring requires 800°C heating in an oxidizing atmosphere, however. Pure CaWO4does not color in the bulk by either reduction or photolytic processes. The observations seem to point to an oxygen vacancy model with possible trapping of two electrons (perhaps an oxygen vacancy in conjunction with two W5+ions).