USDA colour classification
Since colour is an indicator of tomato ripeness, several subjective rating scales and colour charts have been developed for classifying the stage of tomato ripeness. Those included the US standards shown in Table 2. Objective methods of colour evaluation include high reflectance measurement and light transmittance techniques. Determination of pigment content can also be used to indicate tomato colour changes. In order to differentiate between these groups the triangle test methods mentioned above were used.