A symbol refers to a sign, a shape, or an object that is used to represent something else.
They are more sophisticated than signs. This is because symbols need convention to work, that means that people need to agree on the meaning of it, because they usually represent things that have nothing to do with it. In this case, colors represent some moods. For example, usually our culture associates blue with sadness, we all agreed on that. But someone from a different culture can relate that color with joy, we can see those symbols relate to one's culture and history.
