The chief pigments in healthy spinach leaves are chlorophyll a, chlorophyll b, lutein (a xanthophyll) and beta-carotene, which is better known as vitamin A. Spinach also contains a small amount of zeaxanthin, another xanthophyll.
The two kinds of chlorophyll in spinach are what gives it a deep green color. Chlorophyll is the principal light processing pigment in plants. It is capable of converting solar energy into sugar, which the plant uses to live and grow.
The accessory pigments found in spinach also absorb sunlight and help the plant photosynthesize. They broaden the range of light energy, or spectra, the plant can use. Beta-carotene and lutein are both yellowish-red pigments, which means the spinach leaf can use light energy that is bluish to make sugar.
Chlorophyll, in contrast, has poor absorption of yellow and blue light. Chlorophyll a and b cover slightly different spectra, which helps widen the range, but pigments in completely different colors help more.
In terms of nutrition, vitamin A is important for good night vision. Lutein is derived from beta-carotene, and it contains extra oxygen. Lutein has been studied by scientists as an antioxidant and a possible cancer preventative. Plant pigments like lutein also improve immune function, which is very important in people who have compromised immune systems from disease or aging.