It depends on personal tastes and what it's applied on.
For example: I like Blue. I think Blue is cool! But, I also think red is cool, on a sports car. I think it would have to be Red, but thats what I think. The same with orange. Green for a T-Shirt is cool as well!
Remember that if you want to find out what color someone likes, just ask them. Generally though, Red is considered to be cool for most things.
If you are talking about warm and cool colors, a good example of a cool color would be blue. An example of a warm color would be red. The right side of this diagram shows many colors considered to be more cool than warm.
