Despite the potential of online spaces for the democratic development of public discourse, concerns over aggressive and uncivil interactions in those spaces are rising. Online incivility is the term to define the features of a discussion that convey an unnecessarily disrespectful tone toward the participants or the topic. Concerning the adverse impact of online incivility on users, we sought to explore ways to reduce online incivility to promote secure and trustworthy online debate culture. Meanwhile, the web is becoming increasingly multimodal and images are known to be an effective way of improving emotions. The broaden-and-build theory of positive emotions suggests that positive emotions generated by positive images can impact incivility levels. Hence, with the goal to reduce online incivility, we conducted a one factorial between-subject online experiment with three conditions (N = 105). We compared the three conditions (with a positive background image in color, a positive background image in grayscale, and no background image) to identify an efficient way of reducing online incivility. The data gathered from surveys and participants' online comments were qualitatively and quantitatively analyzed to answer the research questions. The results showed that not only positive backgrounds in color but also positive backgrounds in grayscale may be effective in reducing online incivility. The results will pave way for designing more civil discussion platforms in online settings.