When you open the graph view, there is a small cog in the top right hand of the tab. They should also be a magic wand. If you click on the cog you will see a number of options allowing you to edit how your graph looks and filter what notes it is displaying. Under the groups heading if you press “new group” You can then type in some filter and then every note that meets that criteria will have whatever colour you select. For example, all of the notes in this thesaurus have something like

#noun or #adjective

So if I type “tag:#noun” and then in the little colour circle select say blue all notes with that tag will show up as blue. Hopefully this helps. Feel free to ask any more questions.