Relation between B − V color and the stellar mass-to-light ratio in the V band (left), I band (center), and the Spitzer [3.6] band (right) from the population synthesis models of Bell et al. (2003) with their scaled Salpeter IMF (circles), Portinari et al. (2004) with a Kroupa (1998) IMF (squares), Zibetti et al. (2009) with a Chabrier (2003) IMF (triangles), and Into & Portinari (2013) with a Kroupa (1998) IMF (stars). The formula of Oh et al. (2008, Equation (2)) is used to convert between K_s and [3.6]. Note the large disparity between models in the NIR.