20.1.7 Lazy Search Highlighting
When you pause for a little while during incremental search, it
highlights all other possible matches for the search string. This
makes it easier to anticipate where you can get to by typing C-s
or C-r to repeat the search. The short delay before highlighting
other matches helps indicate which match is the current one.
If you don't like this feature, you can turn it off by setting
isearch-lazy-highlight to nil.
You can control how this highlighting looks by customizing the faces
isearch (used for the current match) and lazy-highlight
(for all the other matches). The latter is also used for other matches
inside query-replace.
