Hydroxyethyl cellulose (HEC) doped erbium nitrate films have been prepared by casting technique. The optical absorption was recorded at room temperature in the wavelength range of 190-800 nm. Tauc?s curves revealed a direct allowed transition with optical band gap, Eopt, of 4.40 eV for HEC film, and this value decreases to 4.10 eV for 5wt% erbium nitrate doped HEC sample. The dispersion of refractive index and complex dielectric constants under plasma treatment was also studied. Variation of color parameters composite samples are analyzed in the frame work of CIE L*u*v* color space.