An imaging system color image acquisition including: an image sensor; a tunable spectral filter arranged in an optical path of light propagation towards the image sensor; and a controller connected to the image sensor and to the tunable spectral filter. The controller is configured and operable for generating a colored image by sequentially operating the tunable spectral filter for sequentially filtering light passing towards the image sensor with three or more different spectral filtering curves during three or more corresponding integration time durations. The tunable spectral filter is configured, as an etalon and includes a pair of reflective surfaces. At least one of the reflective surfaces includes a layer of high refractive index of at least n=2.3 or even higher than 3, or a layer of low refractive index, smaller than n=1. The configuration of the etalon provide wide transmission peaks of the spectral curves with full-width-half maximum (FWHM) in the range of about 50 to 80 nm, free spectral range (FSR) of at least 300 nm, and thickness of the etalon in the order to 1 mm or even less.