One excellent and unique feature of Vivaldi browser, that stands out and lacked by other browsers is, the browser adapts to the color of the page and automatically changes its UI accordingly. You can get this feature in Firefox by installing VivaldiFox extension. Not all users are same, different users have different perspectives, if you don’t like the tab coloring feature, you can turn it off easily by visiting settings, here is how that can be done.
Prevent or Stop Vivaldi browser from changing the color of tabs
1. Open Vivaldi, click on V menu> Tools > Settings > Themes
2. Maximize the Settings Window, click on the Pencil icon to edit the theme (default),
3. Uncheck Accent Color from Active Page
4. Give the theme a name and save, you need to be using this as a default theme from now onwards, so that Vivaldi doesn’t change its UI color for every tab/page.