Handling the British National Corpus 

In the menu you will see Tag List.

 

 

If you choose this, having defined and loaded a tag file, you, will see something like this.

 

This window has three buttons, the first of which selects all the tags; the second clears all, and the A button switches between the tag as defined in your tag file, and its description also defined in your tag file. Press A and you will see something like this:

 

 

Switching colours off and on is explained here.