Infrared color‐color plot. Each axis is the ratio of the fluxes at the listed wavelengths. Clusters with a 5.8/3.6 μm flux ratio less than 0.5 and a 24/8 μm flux ratio less than 2 are quiescent. The two color ratios are correlated but with larger scatter in the 24/8 μm ratio than at shorter wavelengths. Objects with flux ratios ﹩F_{5.8}/ F_{3.6}\gtrsim 0.5﹩ or ﹩F_{24}/ F_{8}\gtrsim 1﹩ have infrared excesses. The three objects at the top right of the plot are Abell 1068, Abell 2146, and Z2089 with unresolved red nuclear sources in the IRAC bands indicating the presence of hot dust. These three also have high measured [O III]/Hβ ratios and so probably host a dusty AGN.