Background: Dining out has become increasingly prevalent in China, which is associated with higher intakes of energy, fat and sodium, elevating the risk of diet-related non-communicable diseases. However, evidence on color-coded nutrition labels for onsite prepared meals remains scarce. This study aimed to examine consumers’ perceptions of Dish-Choice, a three-color-coded onsite label, in comparison with the standard Nutrition Facts Label (NFL), to evaluate subjective perceptions of this novel label. Methods: A self-controlled trial was conducted among 3008 diners from canteens in Shanghai, with completing questionnaires twice: first on NFL perceptions, then three months later on Dish-Choice. Logistic regression and paired-sample comparison were used for analysis. Results: Compared with the NFL, Dish-Choice was associated with higher perceptual scores, with greater changes in overweight/obese, males, lower socio-economic status (SES) groups and those with poor dietary quality. Conclusions: The Dish-Choice label elicits more positive perceptual responses across multiple perceptual constructs. It is particularly well-received among vulnerable populations with lower health literacy, including men, lower-SES groups, and individuals with poor dietary habits. This supports its potential as a public health tool for on-site dining settings, though further research is needed to confirm its impact on actual food choices.