An optically black coating on aluminum substrate having improved solar absorption is disclosed along with an enhanced process for formation. The two-step electrolytic coloring process has been used. Porous anodic films have been formed by de anodization of aluminum samples in 16% sulfuric acid. It is followed by black coloration via ac electrolysis in nickel sulfate solution. In this step, we have investigated the effect of chloride and magnesium as additives. Evaluation of the test samples has been carried out by spectral reflectance and nickel content measurements. Choride existance verifies two aspects: the promotion of the coloring process and higher black tones shades are attained. However, magnesium has a minor effect.