If a website is using white text, it becomes difficult to work with it in the default TinyMCE editor since the background is white as well.Visual Composer has a dark mode option which enables dark-colored background for TinyMCE.You can enable it using a toggle below the TinyMCE editor as depicted in the screenshot:
How to enable dark mode in TinyMCE?
How to enable dark mode in TinyMCE?