Biochemical origin of red pigmentation in apples:

• The red skin colour of apples is due to cyanidin 3-galactoside (an anthocyanin pigment). In pomological biochemistry, the colorless precursor substances that undergo enzymatic oxidation and light-dependent glycosylation to form anthocyanin pigments are termed chromogens (or anthocyanidins/leucoanthocyanins).
• Florigen is the hypothetical systemic flowering hormone.
• Carotenoids confer yellow to orange colors, not the deep red of apple peel.
• Flavonoids is the broad class, but the specific precursor product leading directly to red color synthesis is recognized in textbook questions as chromogen.