Different strains of S.aureus = different shades of yellow pigmentation
Two strains of Staphylococcus aureus on Tryptic Soy Agar. Cultivation 24 hours, aerobic atmosphere, 37°C.
Yellow color of colonies of Staphylococcus aureus is caused by a golden coloured carotenoid pigment staphyloxanthin. Pigment production by S.aureus varies from white to orange depending on the strain and the media used. The golden-yellow pigment acts as a virulence factor so generally you can consider yellow pigmented strains to be more virulent.