Betta fish changing color is known as marbling and is due to a genetic trait that determines the fish's color; it allows the fish to change coloration from one day to the next. The jumping gene can affect coloring and then reverse to reinstate the previous color.
Betta fish, also know as Siamese fighting fish, can range in color from red, black, blue, yellow, white and various pastel shades. The males exhibit the broadest array of coloring with ornate fins, while the females are smaller with shorter fins and subdued coloring. Albino betta fish have been documented in rare cases. Some betta fish are iridescent and may appear to change in color. That is due to the coloring being refracted rather than from pigmentation.