In Action Comics #290, Superman and his loyal pup Krypto fly by a comet with a delicious gooey Red Kryptonite center, and get half their bodies all soft and pink.
Reign of the Supermen article on how Superman handles it. But now we're only interested in Krypto.
Meanwhile, in Superboy #98, back when Krypto was younger... The Dog of Steel was briefly involved in Ultra Boy meeting Superboy, and thinking he and Marla Latham were bad guys covering their super-villain outfits with civilian clothes, went on the offensive.
One dog, two colors.