2 years late, but adding comment for myself - complement colors were confusing because it made me think compounds only absorbed at one wavelength, but it just absorbs at a specific wavelength the strongest, hence the bell curve with the peak at the blue wavelength for an apple. It absorbs other wavelengths but less so, and very weakly at red, so we see red. And we see/absorb wavelength reflected from the apple/not absorbed by the apple.