The results of the theoretical and experimental study of the dispersion characteristics of thick reflection holographic grating are presented. The analysis of the diffracted beam intensity is made for the conditions when both the wavelength and angle of the reconstructing wave differ considerably from those used at the recording. The magnitude of the diffracted signal can be described through the joint function of the angular-spectrum selectivity. This is of special interest when the color holographic image is reconstructed with a spectrally wideband light source. In this case the character of the angular-spectrum selectivity function should be taken into consideration for true color holographic image reconstruction.