Arc-eye Hawkfishes come in two color variations. The top photo shows one that is reddish tan with a white stripe on the side. The bottom photo shows a fish that is a darker brown with no white stripe.
According to my fish book, John P. Hoover’s The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals, the white stripe coloring is most common in deeper water where the coral is spaced farther apart. In shallower water, where the coral colonies are closer together, the darker coloring predominates. However, both these photos were taken in shallow water so it’s not an either/or situation.