http://www.famouslogos.org/the-psychology-of-fast-food-logos
http://blog.bullfishgraphics.com/everyday_in_design/fast-food-logos/
red, yellow, orange
{ ... mix em up and you've got the color of vomit! (?) }
Man, I could have sworn we had a post about this before, maybe it's another forum I go to.
But yeah, the psychology behind things like logos can be very complex. I mean look at the starter parameters:
-Simple
-Recognizable
-Direct
That's hard enough to do, but then to add in other factors like colours people associate with certain flavours, fonts that evoke certain moods and feelings, etc. It's an amazing world, and not just limited to food! (automobile branding is similarly nuanced)