I bought Aliquis at a local pet store that I will likely never buy a fish from ever again. The male bettas were all kept in dirty little cups right next to each other. Everyone was dull and listless, fins drooping and hardly moving

. Probably exhausted from flaring at each other and living in their own waste.
Little Aliquis was the one I chose to rescue, because he looked the healthiest and he's blue
Point is, when I got him his fins were really droopy and his color was very dull. His color has gotten brighter, but it's still not the stunning brightness I've seen on other veiltails. He is also very small. I was shocked because I went to visit my mom's betta at her office, who has the same exact tank Al does, and is significantly larger, at least 4 or 5 times the size of Aliquis.
Currently he gets a pinch of BettaMin flakes every night and a pinch of freeze-dried bloodworms every other night. He takes a one day eating break every other week. What should he be getting to improve his color, and should I be concerned about his size?