Colouring in the Worksheet Tabs
If you would like to customise the worksheet tab bar further, you can assign a background colour to your worksheet tabs. This will change the background of the worksheet name, not the worksheet itself.
Step 1
Right click on the tab you wish to assign a colour to. This will bring up a menu with the Tab Colour option in the middle. If you hover over Tab Colour, another menu with colour options comes up. Select the colour you would like to use.

Review
I have chosen a shade of purple so I can show you an example of what a coloured in tab can look like, both if the worksheet is selected and when it is unselected (worksheet name in green and bold font means the worksheet is selected).

