Colorized compiler/linker messages

[Michael D. Norwick]

Good Day,

I have seen this for some time when building ports and was wondering how 
it was done.  GCC when compiling and linking certain programs, ebook for 
example, emits messages in various colors.  How is that done?  Where 
does one find what the various colors are supposed to signify?  Or, is 
it just because it's more appealing?

Thank You,

Michael