The optical absorptance of β′-CoAl in the (0.1-2.5)-eV region was measured and analyzed by the Kramers-Kronig method. The optical conductivity shows interband features beginning below 0.1 eV, with several structures below 2 eV. These structures agree with those calculated from the energy bands of Moruzzi, Williams, and Gelatt. The experimentally observed systematics in CoAl and NiAl confirm our previous interpretation of the spectra of β′-NiAl, and disagree with other experimental and theoretical attempts to understand the optical properties of these compounds.