Fix tooltip colors not initialized correctly

Already committed similar fix (rBbeaed66f292dd) but saw it appearing on
other peoples screens a few times since them. Never was able to recreate
though.
This should make sure everything is initialized fine, so if we see it
appearing again, then it's likely because of manual tweaks or the
version saved in the .blend.

source/blender/editors/interface/interface_widgets.c

@@ -1767,7 +1767,7 @@ static struct uiWidgetColors wcol_tooltip = {
 	{45, 45, 45, 230},
 	{100, 100, 100, 255},
 
-	{160, 160, 160, 255},
+	{255, 255, 255, 255},
 	{255, 255, 255, 255},
 
 	0,