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Herein we report an optical study of surface modified photonic crystals. By growing a dielectric slab on the surface of a colloidal crystal thin film, we increase the penetration depth of a desired range of frequencies within the photonic pseudogap, which is detected by a dip in the optical reflectance spectra of such films. Theoretical description of the surface modified system based on a scalar wave approximation fairly reproduce the experimental results and provide a description of the interplay between the features arising from the presence of the surface slab and the finite size of the photonic crystal. Our work demonstrates that the amplitude of light waves penetrating the crystal with frequencies lying within the pseudogap range can be largely modified by rather simple means.