The really crazy thing is it might actually work ... just accidentally. There's no scientific data saying that blue is the least appetizing color ...
And about one thousand blue M&Ms that call bullshit.
But there is data that suggests it's the most relaxing color, and scientists think you're more likely to eat well if you're relaxed. That makes sense when you look at this testimony from a user. While her appetite wasn't exactly squelched, seeing the world in blue did relax her, and a relaxed belly is a less ravenous belly.
So basically, you could get the same effect by just playing Enya music while you eat. Or, you know, change your diet and try to exercise.