perf tui: Change default selection background color to yellow

Boris reported that 'perf top' is unusable on his default 'black on
white' terminal, which uses (eye friendly) light-grey as a background
color.

The reason is that the TUI cursor for the current selection line uses
HE_COLORSET_SELECTED, and that has a default background color of
'lightgrey' - which is a common terminal background choice and thus
the colors conflict.

Use yellow as the background color instead: that should be an uncommon
terminal background, yet it's still ergonomic on both black and
white/grey terminals.

[ It would be a better solution to straight out detect color
  collisions and resolve them reasonably by converting them to RGB and
  calculating color space distances, but I was unable to find
  proper documentation for SLtt_get_color_object() to recover the
  current color scheme so I gave up ... Yellow works well enough. ]
Reported-and-Tested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20150305103213.GA23046@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/browser.c

@@ -528,7 +528,7 @@ static struct ui_browser_colorset {
 		.colorset = HE_COLORSET_SELECTED,
 		.name	  = "selected",
 		.fg	  = "black",
-		.bg	  = "lightgray",
+		.bg	  = "yellow",
 	},
 	{
 		.colorset = HE_COLORSET_CODE,