Changing the colour of the tabs in Safari on MacBook Pro.

In Safari there used to be a darker shade assigned to the tab currently in use. I don't know when or why... this feature has changed. Now when I have more than one tab open, all tabs are the same color. So then I have to guess as to which tab is the current tab that is open. This is super frustrating as I'm trying to copy and paste links, or otherwise differentiate between tabs.

Do you know how I can make the currently used tab in Safari have a darker or highlighted color? Bonus points if I get to pick the color and customize how dark it is.

thanks!

-John

[Re-Titled by Moderator]