Use zmacs mode. This mode allows for what some might call gratuitous highlighting for selected regions (either by setting mark or by using the mouse). To use, add the following line to your `.emacs' file:
(setq zmacs-regions t)
This is the default behavior.
Pending delete is what happens when you select a region (with the mouse or keyboard) and you press a key to replace the selected region by the key you typed. Usually backspace kills the selected region.
To get this behavior, add the following line to your `.emacs' file:
(require 'pending-del)
(setq isearch-highlight nil)
Note also that isearch-highlight affects query-replace and ispell. Instead of disabling isearch-highlight you may find that a better solution consists of customizing the 'isearch' face.
(setq zmacs-regions nil)