Collaborative governance is increasingly used to address environmental challenges that exceed the capacity of individual organizations. Within the United Nations system, the Greening the Blue initiative represents a system-wide effort to reduce the environmental footprint of organizational operations through coordination and information sharing, coordinated primarily by the United Nations Environment Programme (UNEP). As part of the broader UN system, entities such as the International Telecommunication Union (ITU) participate in these efforts while operating under diverse resource constraints. Although participating entities share sustainability objectives, such differences introduce uncertainty regarding implementation, making facilitation a key element of the collaborative process. This study examines how facilitation shapes collaborative outputs under conditions of bounded rationality, using Greening the Blue as the primary analytical context. An agent-based model (ABM) is developed to simulate repeated interactions among organizational actors, capturing how information sharing and facilitation influence collective outcomes over time. The study demonstrates the usefulness of agent-based modeling for analyzing collaborative environmental governance in international organizations.