A variety of colors can trigger hunger. The most influential colors in terms of food are: red, orange, yellow. [...]
A color psychologist would tell you that this is no surprise: red is the color that makes people hungry. Red instantly attracts attention and it also makes people excited, energetic, and increases the heart rate.
I've heard this a lot, but I have never noticed it working on myself. If it does work, it would have to be a subconscious procedure. Has anyone ever verified this?