Neurophysiological research supports the idea that the appearance of food strongly affects how it tastes to us. Upon the sight of food, activity occurs in the hypothalamus, a section of the brain that controls hunger. Studies have shown that the same cell groups have a reaction to seeing food, just like they do when tasting it. As we grow and our brains develop, they become trained in seeking out food that will provide the best nutrients. Therefore, we naturally choose food that appears to be fresh, ripe, or nourishing. With this in mind, just the presentation of food that does not match our experience could end up tasting unpleasant. For instance, if we were given a purple apple, even if it has the same taste as a ripe red apple, but simply dyed purple, we would likely perceive it to be unpleasant or even rotten.
Also, a food's color can cause us to perceive a taste that is non-existent. When water is tinted red, yellow, or green, our brains recollect the construct it has developed from past experiences with food/drinks of that color. Typically, yellow means a sour taste such as a lemon. Red means a sweet, strawberry type of taste. Finally, green reminds us of an apple or tart type of taste. While all three of these drinks are actually only water with coloring that carries with it absolutely no taste, our brain will likely perceive it to taste differently based on its appearance. This goes to show just how strong of an influence what we see can affect what we taste. Below is a link to a video where ABC news explores how the color of food affects our perceptions of taste: