In the covenant my group are running, vis is transfered into small globes of glass to keep them in one standard form. These globes (Tiny Glass), each hold one pawn.
To add a bit of color, so to speak, I was thinking that the glass in these globes are clear when there are no vis present. When vis is transferred into the globes, they take on a color of the vis, shining out from the centre of the globe.
But here's the question. What colors should the different Arts have? Any suggestions? Are there any official answer to the color of the Arts? I can't place it, but I think I remember reading about this somewhere. Can't remember where, though..
It's in the description of "sense the nature of vis" (at least it is in 3rd, 4th and 5th editions, it's not in first or second eddition)
from page 158
Muto constanty fluctuating
Corpus dark red
Imagonem pearly blue
Ignem bright red
Terram dark brown
What's nice about this is you can introduce subtle changes to the color or appearance based on mystical alignment. So perhaps fairy vis 'pulls' towards the user, or infernal vis bubbles like it's boiling. Divine Vis always has a perfect color and magical vis, well I'll leave that one up to you.
Also, you can occasionally introduce something that doesn't fit into the system. An odd ball. Maybe, because Magic is an Art an not a science it's just different. But maybe, maybe it's something unique and special. Do the players risk the time to find out the difference? If it is unique, how so? Is the source of the vis unique? All sorts of adventures could develop simply around noticeing the attributes of vis.
IMS we have a similar system using small stone tokens marked on one side with the symbol for the type of vis, small, easy to carry and easy to identify. Also durable (handy for travel).