We show that ultrathin metallic films deposited on porous anodic alumina (PAA) templates can enhance the reflection at certain wavelengths in the visible range, due to Fabry-Perot optical interference. The reflectance spectra can be tuned in a broad range by tuning the structural parameters of PAA including its pore depth, size and porosity. This results in tunable, iridescent colors of the films that can be spatially patterned. A refractometric chemical sensor is designed to convert the change in effective refractive index into the change in the reflectance spectra, which leads to color change discernible by naked eyes. This opens up the possibility for easy-to-operate chemical sensors with extremely low cost. (C) 2015 Elsevier B.V. All rights reserved.