If you have CC, and not DWCS6, the preference is under Edit > Preferences > Code Coloring > Enable tag highlighting checkbox and color setting
The problem you describe is normally the result of an error that DW can't work around, like an unclosed <title> tag.
Run your page through the validator at http://validator.w3.org to clean up any code problems, it should come back after the code is repaired
I tried what you said but Edit > Preferences > Code Coloring > ""Enable tag highlighting checkbox and color ""setting doesn't show up !
Are you sure you have DWCC and not DWCS6 Cloud (both are available under the same subscription)?
Go to Help > About Dreamweaver and check your version and build.
Tag highlighting wasn't available in DWCS6 (version 12.x).
If you do have DWCC, version 13.x or later, you may want to clear the program cache, restore preferences or do a clean re-installation (in escalating order)...