Pigments are molecules that selectively absorb particular (ranges of) wavelengths of light. The remaining reflected wavelengths are the color that you perceive the pigment to be. So pigments can only subtract wavelengths of light from the spectrum, but they cannot generate their own light. For example, a blue pigment absorbs red and green light, but reflects every other color. Alternatively, the blue pigment might only absorb orange light, which is the color complement of blue.