Pigments are compounds in plants that give it color. They absorb certain spectra of light and reflect others. For example, chlorophyll reflects green light. Particularly intense reflection will augment the color of the plant. Spinach pigments serve a variety of functions for both the plant and those who consume spinach.
Chlorophyll is the green pigment in most plants that is associated with photosynthesis. The pigment absorbs all colored light except for the green band, which it reflects to give spinach its characteristic leaf and stem color. "Chlorophyll a" is a strong blue-green color and primarily responsible for photosynthesis, while "chlorophyll b" is a supporting photosynthetic pigment, according to University of Wisconsin Chemistry.
Carotenoids are especially useful to humans since they are broken down in our bodies to become Vitamin A, an essential nutrient for health and survival. They are typically yellow-orange pigments that give carrots their characteristic color. Beta carotene is the primary carotenoid pigment found in spinach.
Similar to chlorophyll in structure, pheophytins are actually decomposition products. They are "spent" chlorophyll that has lost an ion but which remains in the leaf and continues to lend the leaf its color. The ion lost comes from the magnesium component.
When carotenoids become oxidized, or take on an oxygen molecule, they are known as xanthophylls. The name changes since their structure has changed. These pigments are still yellowish in color but not reddish or orangish the way that carotenoids often are.