A color composite of the W51 region with major regions, W51 A, B, and C, labeled. W51 A contains the protoclusters W51 Main and W51 IRS 2; these are blended in the light orange region around 49.5−0.38. The blue, green, and red colors are WISE bands 1, 3, and 4 (3.4, 12, and 22 μm) respectively. The yellow-orange semitransparent layer is from the Bolocam 1.1 mm Galactic Plane Survey data (Aguirre et al. 2011; this paper). Finally, the faint whitish haze filling in most of the image is from a 90 cm VLA image by Brogan et al. (2013), which primarily traces the W51 C supernova remnant. This haze is more easily seen in Fig. B.6.