An exploratory study has been conducted in which 12 students in Bachelor of Science in Psychology were asked to use the Visu reflection tool during Computer-Supported Collaborative Learning (CSCL) situations. Visu is a web videoconferencing platform that allows participants to put reflective markers during their collaborative learning activity, and to review the traces of their synchronous collaboration later. In this study, co-learners used two types of markers: (1) free markers and (2) socio-emotional markers to express either negative or positive feelings about the way they collaborate together. Our contribution is related to the first focus of the workshop: emotion awareness in CSCL. In line with this focus, our main questions are as follows: (1) How can the Visu tool help learners express and share their feelings about collaboration? How does this affect the way they interact and learn together? (2) How do they use the Visu markers after the collaboration to self-reflect on their group processes? In this paper, we first describe the Visu platform. We then present a study we have carried out to answer the questions presented above. We finally conclude with the contributions of our research to the workshop topic.