My bettas change color like I change clothes(about every 3 days). I had a nice solid red crowntail go from that deep red, to pink, to irridescent blue, to red, then to white with red fins. He really confused me....damn thing still does. He doesnt know what he wants....I secretly think "he" ended up being a she with really long fins. You know girls, cant fiure out what they want!
My blue veil rescue started to turn red when I gave him color enriching foods. I only use them to get him off bloodword/pellet staples.
If you really are worried, check levels, and do a 15% water change every couple days. Try raising the heat a bit to kill off any infection, and add AQUARIUM SALT to the tank(or add a bit more over the doseage if you already are) to help keep the parasites/cysts at bay. I have seen people put bettas at like 90 degrees for an hour or so a day to try to kill off infection, im not sure how that works out...but im sure you could get away with setting at 84 and raising to 88 while keeping a close eye on him