Social media platforms provide rich signal sets to understand the nature of social life, and sentiment analysis techniques have been developed to understand the emotional content of text from sites like Twitter and Facebook. Beyond text however, most social media platforms have images at their core, and communication of images may require quantization. Here, we develop methods and present results on understanding the association between the visual content features of images on the popular social media platform Instagram and the psycholinguistic sentiment of their hashtag descriptors. In particular, we collect several thousand images and analyze several aspects of color to predict image sentiment. These results affirm and clarify several psychological theories on the relationship between color and mood/emotion, such as colorfulness being associated with happiness. The data-driven psychovisual insights into sentiment developed herein can be used to define novel fidelity criteria for designing color quantization schemes.