How to disable highlight similar variables?

Settings | Editor | Colors &  Fonts | General

Have a look at "Identifier under caret" (2 entries) and maybe also "Search result" (2 entries)

Thank you. I understand the color settings but what about turn off highlight function?

There is no such switcher/option. If every single functionality can be turned on/off then you would probably see 2-3 more setting pages in Settings compared to what it is now.

Removing colors makes the same result as turning it off -- no real need for additional separate option.

Try to switch to Power Save mode (under the File menu).