Variable Parrot Fish, colour. Callyodon mutabilis. Marshall's "Tropical Fishes of the Great Barrier Reef" (1966) p.321-322

Artwork by George Coates
Parrotfishes are a group of about 95 species. They are found in relatively shallow tropical and subtropical oceans throughout the world, displaying their largest species richness in the Indo-Pacific. They are found in coral reefs, rocky coasts, and seagrass beds, and play a significant role in bioerosion.
Description source:
Wikipedia
View the original image at the Queensland State Archives:

Digital Image ID 5938