Anhydrous ${\mathrm{Co}}^{2+}$ compounds and hydrated ${\mathrm{Co}}^{2+}$ compounds abosorb red and blue/green radiations, respectively. The colour of these compounds respectively are

The colour is complementary colour to the colour absorbed by the compound. Hence, the colours of anhydrous and hydrated ${\mathrm{Co}}^{2+}$ salt will be blue/gree and red, respectively.