Color-tunable LED luminaires are a nascent and growing product category. Beyond the inherent energy efficiency of LEDs, these luminaires offer other potential benefits including improved health and well-being, increased productivity, enhanced mood or alertness, and higher occupant satisfaction. Consequently, there is reason to believe that color-tunable luminaires will gain market share. At this point, however, it is important to understand the potential tradeoffs, limitations, and issues surrounding this emerging product category, so that the industry can work together to address challenges needing attention as these products mature. DOE evaluation of color-tunable products demonstrates the variety of approaches that different manufacturers use to achieve color tuning, and highlights the challenges involved in testing, controlling, and specifying color-tunable products.