The dark mode comes with a toggle that allows you to switch it off. As such there are no additional changes in terms of design. However, when you apply the new theme, the user interface becomes darker. The colour isn’t really black but it is more like a dark grey.
Here’s How to Turn on YouTube Dark Mode for Android
Note that the feature is being rolled out gradually. So if you haven’t received the feature yet, you should in the coming days. Here’s how to enable YouTube dark mode on your Android phone.
Also Read: Youtube Dark Mode Rolls Out For Android Users