The principal sources of errors in colour reproduction of the banana tube are the colour phosphors employed, the finite spot size of the tube and the self-decoding colour circuits. The errors due to these causes are analysed, particular attention being given to the use of an incorrect green primary phosphor and to methods of evaluating the importance of random errors in the chromaticity and luminance of the phosphors. Methods of alleviating errors due to the incorrect green primary by special correction circuits are discussed.