Color functions on many more levels than that of decorative purposes.  The colors we see in our environment are perceived both objectively and subjectively.  I believe there are two crucial roles color plays in the human environment.

Color as influence from a psychological aspect:  How does this environment make me feel?

Color as information:  What does this environment tell me?

Eighty percent of the information we receive is through our physical environment.  If color belongs to the environment (which it does) then it should serve as a means of information to help us understand both the natural and artificial (architectural) environment.