Washington system photometry of M31 clusters classified by Caldwell et al. (2009, 2011), with blue representing clusters with ages t ≲ 2 Gyr, and red designating globular clusters, t ~ 14 Gyr. On the left is a two-color diagram; on the right is a histogram of C − T ₁ colors. In the absence of a spectroscopic or HST imaging age designation, we classify systems with C − T ₁ < 1.2 as young, and C − T ₁ > 1.2 as old.