Priming effects are out of fashion now, but I can see how a bright-colored food could make a child more excited than a plain-colored food.
Those studies failed to replicate, but some people still believe in them because they are so intuitive, they seem to match their personal experiences. Like seeing kids go hyperactive after eating candy because candy reminds them of Christmas and Halloween and birthday parties and other occasions in which they are allowed to play and be noisy.