Colour and spectral imaging systems typically use filters and glass prisms to disperse light of different wavelengths. With the miniaturization of integrated devices, current research on imaging sensors focuses on novel designs aiming at high efficiency, low power consumption and slim dimension, which poses great challenges to the traditional colourant-based filtering and prism-based spectral splitting techniques. In this context, surface plasmon-based nanostructures are attractive due to their small dimensions and the ability to efficiently manipulate light. In this article we use selective conversion between free-space waves and spatially confined modes in plasmonic nanoresonators formed by subwavelength metal-insulator-metal stack arrays to show that the transmission spectra through such arrays can be well controlled by using simple design rules, and high-efficiency colour filters capable of transmitting arbitrary colours can be achieved. These artificial nanostructures provide an approach for high spatial resolution colour filtering and spectral imaging with extremely compact device architectures.