Colouration is an unwanted effect in rooms for speech and music. While very easy to hear when present, it is difficult to measure objectively. Examples of colouration problems include orchestra stages with suspended overhead reflectors, meeting rooms and talks studios with parallel hard walls. While colouration can easily be detected by listening, it is difficult to measure objectively. The cepstum technique is suggested as a method that can indicate a possible problem with colouration. The method has been applied successfully to a number of examples not only with measurements, but also by analysis of simulated impulse responses.