Final answer:
When talking about pigments, we use the term subtractive color because pigments work by absorbing certain wavelengths and reflecting the rest, creating colors by the subtraction of light. This differs from additive color, where colors are created by adding light of various wavelengths together to achieve white light.
Step-by-step explanation:
We talk about subtractive color mixing when referring to pigments because this process involves the absorption and removal of certain wavelengths of light, which effectively 'subtracts' colors. When pigments mix, each pigment absorbs certain wavelengths of light and only the unabsorbed wavelengths are reflected back to our eyes. For example, a pigment that absorbs red and green light will appear blue to our eyes because blue is the color that is not absorbed and, therefore, is reflected. This is different from the additive color process seen with light sources, where colors are created by adding together different wavelengths of light. White light, for instance, is a result of combining all the colors of the visible spectrum in equal proportions.
Why do we say subtracting instead of addition in the case of pigments? Because pigments work by subtracting certain wavelengths of light, while the color perceived is the result of the combination of all the wavelengths that are not subtracted. For instance, mixing blue and yellow pigments will absorb red light, resulting in green as the color that is not absorbed and therefore seen. This is in direct contrast to additive color mixing where red, green, and blue light can be added together to achieve white light.