Many languages have only one term for “green” and “blue”, generally called “grue”. Since they are especially spoken near the equator, Lindsay and Brown (2002) suggested that “grue” categories are caused by lens-brunescence, resulting from chronic exposure to high amounts of UV radiation. Due to increased lens aging bluish colours should appear greenish. Monitor-simulation experiments supported this hypothesis. However, the distribution of “grue” foci (Regier & Kay 2004) and the adaptation to lens yellowing in older observers (Hardy, Frederick, Kay & Werner 2005) contradicted the lens-brunescence hypothesis.This study reinvestigated the possible influence of aged, brunescent lenses on colour categorization, simulating aged lenses by means of filters. The filter simulation shows important differences to previous monitor simulations, and defuses arguments that were put forward against the lens-brunescence hypothesis.