Since version 2.1, WebStorm & PhpStorm both come with a new code highlighting feature. It makes it easier to work with big and complex HTML files, with deep nested tags structure:
Please note that highlighting is only activated when there is more than one tag with the same name in the hierarchy.
By default, only 6 parent tags are highlighted with 6 different colors. You can change the depth to highlight or completely disable the feature in Settings | Editor | Appearance | Enable HTML tag tree highlighting.
Also you can tweak the colors in Settings | Editor | Colors & Fonts | HTML.