Press Command+Shift+Space (or Ctrl+Shift+Space) to flip through tab icon colors.
On any tab you have open, you can change the color of the tab's icon to any color you've defined. Giving you the control to highlight important tabs and never lose focus of which one is which.
Using the Customizer tool, you can add as many, or as little, color choices as you desire. Pick the colors you like, in any order that works for you!