This question pertains to the condition known as synaesthesia. This condition describes how our senses work together. For example - with respect to sight, taste and smell - seeing a color may evoke any number of other sensations. Green may be evocative of the smell of grass, lemon yellow may evoke a sour taste.

This is best understood by the fact that each sense has a pathway to the brain. These paths are parallel to each other.

However, in some situations, a cross over from one pathway to the other occurs. Seeing the color yellow-green may evoke taste sensations of sourness; pink may evoke sweetness. Seeing the color grey may evoke olefactory (smell) sensations of smokiness.

We all have some degree of synaesthesia. However, a person with a strong sense of synaesthesia senses stimuli different from a "normal" person. For example, to the person with synaesthesia, a color might have a "taste", a sound might be "felt", and a food might be "heard".

Here are some web sites that will provide much more information :

Blue Beef and Violins
The taste of beef, such as a steak, produces a rich blue. When she hears violins, she also feels them on her face.

How color affects taste
Science Project - Easy to understand student project

Synaesthesia - Doctor Hugo || Museums of the Mind ||
New media org. for art & mind research
Belgian Synaesthesia Association [BSA]

The International Synaesthesia Association
(University of Cambridge)

Synesthesia in Art and Science
MIT

Synaesthesia ( Links and references)
Letters + colours
Sounds + synesthesia

Color and Odors