Urban waterways are facing intensifying pressures from population growth, densification, pollution, and climate‑driven hydrological change. Although a wide range of decision‑support tools exist, many waterway and stormwater decisions remain constrained by governance silos and narrowly framed project scopes. This fragmentation limits the ability of managers to recognise system‑wide interactions, identify emerging risks, and capture opportunities for integrated outcomes. This research introduces a new visual heuristic—based on additive RGB colour coding—to support more coherent and strategic decision‑making across urban water systems. This framework offers a simple but powerful way to visualise trade‑offs and interactions that are often hidden within technical assessments. The RGB approach can be overlaid onto existing prioritisation tools, triage systems, and ecological return‑on‑investment models, enhancing their communicative clarity and supporting more transparent cross‑agency dialogue. Early application suggests that colour‑based synthesis helps practitioners and stakeholders “see” the broader system context, improving alignment between stormwater, biodiversity, and infrastructure planning. This paper proposes RGB colour coding as an accessible, integrative layer that can strengthen decision‑support for resilient, liveable waterways.