This theme has been deprecated in favour of the official Google Chrome dark theme.
Incognito mode currently uses a dark colour scheme to distinguish it from normal mode. This theme imitates that colour scheme and applies it throughout the whole browser.
This theme is fully open-source under the Apache License. Check out the source code on Github - https://github.com/Fiddle-N/material-incognito-dark-theme/.
Chrome theme devs currently have no ability to colour the omnibox. As a result, the omnibox will always be white.
To uninstall this theme, go to Settings, scroll down to the Appearance section, and next to "Themes - Material Incognito Dark Theme", click Reset to Default.