I don't know if it was just me, or if I didn't account for the nature of the blueberries, but one time I did a 5 gal batch of bavarian Hefe
I bottled 3 gallons, and racked one gallon on strawberries and another on blueberries (red wheat and blue for the fourth of July)
Anyways, the plain hef and the strawberry hef carb'd nicely, but the blueberry one never carbonated. Idk if it was the acidic nature of the blueberry, or if I did something wrong.
But if it has something to do with blueberries, then I'd let the beer ferment, then add the food coloring and bottle.