These colours in vegetables are due to zeaxanthin and lutein, both pigments that belong to a group called xanthophylls, which in turn are a member of the carotenoid family. They bring about yellowish colours, even though many times they are hidden by the green colour of chlorophyll, e.g. in spinach or avocado.
Apart from the beneficial properties of carotenoids previously described, these two compounds are very important because they selectively accumulate in the retina. Different epidemiological studies have shown that lutein intake and serum levels are associated inversely with risk of ophthalmologic diseases associated to aging, such as cataract or macular degeneration (Aguilera Garca, C. M., et al.).