The usual way to apply coloured labels to files and folders in the Finder is to go to File > Label (or right-click). But you can also apply labels from the keyboard.
To start, if the Label button isn’t yet on your Finder’s toolbar, go to View > Customize Toolbar. A dialog box will open entitled Drag your favorite items into the toolbar. Click Done. Next, launch System Preferences, select the Keyboard pane, and open the Keyboard Shortcuts tab. Choose Application Shortcuts, and then click on the + button.
In the Application drop-down menu, select Finder. In the Menu Title field, type the name of your shortcut’s colour, entering it exactly as it appears in the Finder’s Label drop-down menu (Red, Orange, Yellow, and so on). Finally, set a keyboard shortcut for each colour (Control-Shift-1 to Control-Shift-7, say, for the seven colours).
Unfortunately, there’s a catch to this tip: to make the keyboard shortcuts work in the Finder window, you must have first opened the Label toolbar menu at least once in that Finder session.
If you assign a keyboard shortcut to the different colour labels in the Finder, you won’t have to use your mouse to access the Label menu
There is, however, an alternative – you can create an Automator service that will do much the same thing. Launch Automator, click Service and then Choose. In the Services receives selected drop-down, choose Files Or Folders. In the search box at the upper left, type Label to find the Label Finder Items action. Drag the action to the right side of the Automator window. Choose a colour you want to use, then click Cmd-S to save your service.
Next, return to the Keyboard Shortcuts tab in System Preferences of the Keyboard preference pane, and select Services in the left pane and your new service on the right – it will be in the Files And Folders section. Press Return to activate its shortcut box, and type the shortcut you want to use. While you’re there, make sure that your new service’s checkbox is selected.