Anomalous colour vision exists in one out of 12 Caucasian males. Three analysands are described who became aware of their defect only in adult life, and the meaning of colour blindness to a fourth with normal vision is reported. An attempt is made to comprehend some of the developmental consequences of the defect and of the successful effort to prevent awareness of it both subjectively and by others. It is claimed that colour defect operates as an independent factor that may exacerbate a sense of uncertainty either or both in the form of tendencies to doubt and of insecurity in object relations.