The enhanced Fabry–Perot (F–P) resonance caused by adding a layer of AlN film to different metal substrates (AlN/metals) was analyzed by controlling the thickness of AlN film. The obtained results using the finite-difference time-domain (FDTD) method show that the absorption capacity of visible light was changed by the film interference effect. Then, the light absorption of Au/AlN/Fe (AAF) trilayer structures exhibits that the addition of the ultra-thin Au layer to the AlN/Fe surface improves the light absorption, the color gamut, and purity. Both the transfer-matrix theory and Fresnel–Airy equation were used to compare the FDTD simulations, the calculations show that all the results are consistent. Systematic analyses revealed that AlN film as an F–P resonant cavity is a promising strategy for optical applications, and AAF is an ideal structure in the applications to optical filters, no-ink printing, and optical anti-counterfeiting.