Firms increasingly rely on images to drive user engagement with their social media content. However, evidence is limited on when and why image characteristics can draw social media users’ attention and increase engagement. In this research, the authors theorize that color complexity in images can serve as an external cue that draws social media users’ attention and provokes a shift from the peripheral processing mode to the central processing mode. This shift can result in deeper processing of the social media post that features the image, thus increasing the likelihood of the users’ engagement with the post. They further reveal heterogeneity in the effect of color complexity due to the time of day when the users are exposed to the image, image height, and sentiment and complexity in the text accompanying the image. The results are consistent across an empirical analysis of two proprietary Facebook datasets from distinct industries and time periods and confirmed by two biometric eye-tracking experiments that provide process evidence. The findings have important implications for both content marketers and academics as they seek to identify content features that can maximize user engagement on social media.