The present invention relates to genes, and markers therefor, involved in lutein production in cereal plants such as wheat. In particular, the invention characterizes .epsilon.-cyclase and phytoene synthase genes from wheat. Furthermore, the present invention relates to the manipulation of .epsilon.-cyclase and/or phytoene synthase expression to alter colour traits of a plant which can effect the characteristics of food and/or non-food products obtained from said plants.