For example, if we shine white light through a green filter, only the green light passes. Red and blue are absorbed. Remember that combining red and blue light produces magenta. So you can think of the green filter as absorbing magenta. A filter passes its own color and absorbs or blocks its complement.
Red filters pass red light and absorb cyan.
Cyan is a combination of green and blue. Blue filters pass blue light and absorb yellow light. A blue filter subtracts red and green from white light. Filters produce color by subtracting wavelengths of light.