I like this idea John 
I posted something similar here:
Having more tag colors would be extremely useful, as a general tool.
In respect of part of speech, my preference would be that the part of speech be automatically identified by LanguageReactor (which can already do this), rather than have to manually tag the part of speech. And then possibly LanguageReactor can also supply functionality to set colors for each part of speech.
But for me, as long as the part of speech is identified, it’s a fairly trivial issue to add color (since I download it and add my own CSS).
An example is in the image below, where I’m identifying certain articles & prepositions and adding my own color via CSS (in addition to using the in-built tags which show up as a yellow highlight color):
