Novel nanohole arrays with volcano-shaped holes (truncated cones) are reported to obtain structural colors with excellent purity without using index-matching layers. They further show efficient sensitive environment responses. The novel structures are fabricated via a low-cost, large-area colloidal lithography method. Numerical simulations demonstrate that each nanovolcano, comprising one upper hole and one lower hole, excites two surface plasmon resonances (SPRs), generating only one single transmission maximum at a tunable position (monochromatic color), and calculations show excellent agreement with the measured spectra. Three primary red–green–blue (RGB) monochromatic colors are obtained by adjusting the lattice constant. Moreover, the colors can be tuned easily and inexpensively across the whole visible range, retaining a single sharp transmission peak, showing an efficient responsive color display. Because of the simple fabrication process and remarkable properties, Ag nanovolcano arrays are believed to be greatly advantageous for sensors, optical devices, color displays, and nanoantennas. Furthermore, the novel structures can be used as versatile substrates for cell biology, analysis of single protein molecules, and surface-enhanced Raman scattering.