FAQ: "Does the USDA make color tubes, similar to the OJ PLASTIC COLOR TUBES but for GRAPEFRUIT juice?"
The Citrus or OJ Scores was designed and optimized for orange juice and that is the only scale that has physical standards such as the OJ Tubes to check and validate the scale. There is a long history with orange juice color evaluation and product quality. Before orange juice color was evaluated instrumentally, these OJ Tube standards were used to evaluate the color visually.
Yes, Citrus of OJ Scores have been used to quantify the color of tangerine, red grapefruit. white grapefruit, lemon and lime juice because the color of these juices is a combination of yellow and red. They are not the intended use of the scale however, and the user has to find their own range of acceptability with these juices in terms of CR, CY, CN. It is a non-standard application.
The reason why there are no physical visual standards for these alternate juice types is cost. To develop and maintain any visual color standard system has an annual cost. These days, the USDA does not have to budget to do it on their own but expect considerable help from industry. Industry has not stepped up. So the Citrus Scores and visual standards remain the only option for all to use in standard and non-standard applications of measuring juice color.