Questions like that one are obvious nonsense. It is like asking "What is the colour of jealousy?" Richard Dawkins likes to use that question to answer some of the non-questions that theists ask him in order to try to trip up rational thinkers.
Some questions simply can't be answered, and just because they can be phrased semantically does not mean that they are meaningful questions.
|Envy is green - not jealousy!|
Incidentally, "Green" is not a good answer. Can't you tell the difference between envy and jealousy? Anyway it was only ever a metaphor, and metaphors are second only to analogies in the search for the truth. They might be useful teaching aids but they are rarely true.
To use another example, you might just as well as 'what is the colour of Middle C'?
|What is the colour of Middle C? (Picture from here)|
Synesthetes might be able to give you an answer. They mix up the senses and some of them really do taste colours and smell sounds and even see musical notes as colours. I doubt you would get a consistent answer from a group of them though.