Japanese names are always really cool for Betta. I took Japanese for 5 years and find it to be a beautiful language especially if you want something descriptive that doesnt flow in english but does in Japanese. For example, my fish, as you can see by my signature, is named Akashi. This means: "red death" hahahahah.
Colors you could use would be: 1.aka-red, 2.ao-blue, 3.kiloi-yellow, 4.murasaki-purple, 5.kuro-black, 6.shiro-white, 7.midori-green, etc.
Also some interesting words to put them together with could be: 1.shi-death, 2.enma-devil, 3.hana-flower, 4.akuma-demon, 5.momo-peach, 6.ame-rain, 7.tsuki-moon, 8.hoshi-star, 9.yama-mountain, 10.mizu-water, etc
I hope that helped!