The current code for detecting whether colors should be used by default
was not working. Normally what programs such as git or grep do is check
if they are writing to a pipe.
To see the issue by yourself:
$ BOARD=samr21-xpro make -C tests/periph_qdec > I_SHOULD_NOT_HAVE_COLORS 2>&1
This commit uses MAKE_TERMOUT, MAKE_TERMERR and if ANY of them is NOT
a terminal, colors are disabled.
0d6a8879bc