Hot chocolate tastes better in an orange cup

This is like beer tastes better when served in mugs by Hooters girls rather than drinking the same beer from a can you bought in the conbini.

Orange color is is said to be associated with food. Even in language, the word describing orange color also means a fruit (I know it works for Polish and English, not sure about the Japanese). Orange dishes boost hunger. If you want to eat less, you should eat on a blue dishes - blue color is associated with unhealthy things.

If someone is interested in this particular topic, the psychological influence of colors, there is a whole specialization of psychology called the "color psychology". It's quite popular in Europe.