perf ui browser: Return the current color when setting a new one

perf ui browser: Return the current color when setting a new one

Tools that want to change parts of the line to a different color and
then restore the previous one will use this, starting with the annotate
browser that will change the color of addresses if not on the current
entry, i.e. the selected one.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-uiajpevhxo4mzrvna6remb4a@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>