[cfe-users] Why doesn't clang use colors for diagnostics by default?

[Victor via cfe-users]

Hello, all.

Why doesn't clang use colors for diagnostics by default?
My environment:

$ cat /etc/*-release
Red Hat Enterprise Linux Server release 6.3 (Santiago)

$ echo $TERM
xterm

Doc here 
http://clang.llvm.org/docs/UsersManual.html#formatting-of-diagnostics 
says: "This option, which defaults to on when a 
color-capable terminal is detected". Isn't xterm "a 
color-capable terminal"?

If I give -fcolor-diagnostics explicitly, all works as 
expected. But why must I do that? GCC uses colors by 
default.