b) As (a) above, but applied directly to the stimulus or the source (primary or secondary) giving rise to the sensation. (For brevity, the stimulus is often referred to as the colour).
c) The property of an object or stimulus or quality of visual sensation, distinguished by its appearance of redness, greenness, etc., in contradistinction to whiteness, greyness, blackness (i.e. chromatic colour is contradistinctinve to achromatic colour).