It is known that porphyrins are colored compounds, whereas porphyrinogens are colorless compounds.What is the chemical difference between porphyrins and porphyrinogens that accounts for this difference?

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Porphyrins have a macrocyclic ring structure that is completely conjugated (i.e., alternating double and single bonds), meaning that these compounds are highly unsaturated.This conjugated (or unsaturated) nature of the molecules results in these molecules being highly colored.When porphyrins are reduced to porphyrinogens by the addition of protons across some of the double bonds, the degree of saturation is increased, causing these compounds to become colorless.

It Is Known That Porphyrins Are Colored Compounds, Whereas Porphyrinogens