Collective reflection is essential for teachers' professional growth which involves multiple individuals participating in reflective exercises. However, collective reflection often faces problems such as disorganization and inadequate criticism. This study utilized the six-hat thinking framework to structure collective reflection among pre-service teachers during project-based instructional design learning. Despite its known collaboration-boosting effects, the impact of six-hat thinking technique on pre-service teachers' collective reflection, particularly within co-regulation, is under-explored. Focusing on Blue Hat's coordinating role on monitoring and planning, this study employed co-regulation coding and Lag Sequential Analysis (LSA) to analyze collective reflection behaviors. Findings uncovered co-regulation patterns within the six-hat-enhanced reflection, emphasizing Blue Hat's significance. This study distinguished regulation patterns between high and low-level understanding on grasping the six-hat thinking technique. High-understanding groups demonstrated co-regulation centered on regulation-evaluation, fostering self-assessment of instructional design projects and refinement planning. Conversely, low-understanding groups exhibited a pattern focused on task verification, neglecting group work regulation or evaluation. This study also delved into LSA-derived empirical insights on communication dynamics underlying co-regulation in six-hat-integrated collective reflection.