A study says so; it must be true:
In general, how people perceive taste is influenced by many factors unrelated to the actual food. Past studies have shown that the color of the plate, the price on a bottle of wine, and the verbal description of food can affect people’s enjoyment of dishes and drinks alike.
To see how hot chocolate enjoyment was affected by cup color, Piqueras-Fiszman and her colleagues asked 57 participants to rate samples of the same delicious beverage in four colors of plastic cup: white, cream, orange and red. (All cups were white on the inside.)