Each colour within the visible light spectrum has its own narrow band of wavelength and frequency. Red has the longest wavelength and violet the shortest.
When light reflects from a smooth surface in a single direction, this is specular reflection. A rough surface causes scattering of the light in many directions, which is called diffuse reflection. Objects that transmit light are either transparent or translucent.
A colour filter works by absorbing some wavelengths and transmitting others. A red filter transmits red light and absorbs the other colours. The colour of an opaque object depends on which wavelengths are most strongly reflected. The other wavelengths are absorbed. A red object reflects red light strongly and absorbs the rest. If all wavelengths are reflected equally the object looks white. If all wavelengths are absorbed it looks black. A blue object viewed through a red filter looks black, because the red filter absorbs the blue light, so none of the light reaching the eye comes from the object.