it's not to fool the naked eye but the periscope instead

USS Boxley (1918)

Above US merchant ship, the USS Boxley (c1918), showing its World War I dazzle camouflage scheme (Type 10 Design I), which consisted of four colors: Black, gray-white, blue, and blue-gray.

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Helen Johnson Keyes, OUR MIGHTY SENTINEL CITY: She Stands with Naked Sword and Bayonet to Defend You and Me, in Farmer’s Wife, 1 July 1918, p. 31—

—what a strange object is that, over there! It is painted with curving, wavelike stripes of yellow, pink, lavender, blue, broken up by sudden splotches of other colors. 

It is a camouflaged vessel—a vessel to which has been applied what we call in the case of animals, “protective coloring.” It has been painted so as to blend with the sea and sky when seen at a distance through the eye of a submarine periscope. The camouflage does not conceal the boat from the naked eye which views it almost from its own level but to the periscope seeking it…the vivid, curveting stripes are thereby confusing…

Note There are no full-color photographs of WWI ship camouflage. The above image, from a black and white US government photograph in public domain, has been "digitally colorized” using AI software. While its light / dark values are accurate, the choice and location of colors, even when plausible, may not be literally correct.