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.

Not sure what you're comment is about. The visual stimulus wouldn't have any effect after the stimulus is no longer present.

That's the part I say went out of fashion. The scientific consensus used to be that a stimulus can subconsciously influence you for a while. Like if you saw an ad targeted towards old people you'd subconsciously fix your posture and walk with a straighter back for a little while after you saw the ad.

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.