|Mr. Moto's bright coloring (left) & stripes and dull coloring (right)|
I also have not changed his diet, he loves to eat the Aqueon Color Enhancing Tropical Flakes and he will really make a pig of himself. He also prefers to eat flakes while they are still floating on top the water, which makes me wonder why Betta pellets are generally what is given to them via pet-store Betta food since they tend to sink to the bottom quickly.
Other people have suggested that these horizontal stripes are "stress stripes" but I really don't see that being the case because he'll change back and forth randomly which seems more mood based than anything. To me signals of fish stress would be...gasping for air, clamped or rapid movement of fins, irregular swim pattern, loss of appetite, pale coloring, etc.
I do wonder if it is either a mating or defense mechanism of camouflage that spikes these color changes. Or perhaps it is just a characteristic only shown in some Betta's as I have read that this is more likely to happen in iridescent colored Betta's. However, I'm not sure Mr. Moto is considered "iridescent". I am not sure why this would be mating related in his case as there are no other Betta's around for him to compete with or for.
This color change seems to happen from when he gets excited to when he is in a sleeping stage. He turns a vibrant blue shade when he knows I am paying him attention and he may be getting food (his excited stage). However, when he is in a deep sleep his colors tone down and he develops a dull body color with dark stripes. He also has an in-between color variation of both during these mood changes where the top half of his body will be blue but there will be some dark striping coming through the middle lower half of his body. This would more than likely come in handy during mating courtship where the colors would be bright and vibrant (excitement stage again), and as a defense mechanism to camflouge when he is at a more vulnerable stage (ie. sleeping) and the colors would dull into his stripe stage.