What I've done is make up a PDF using Adobe InDesign. I would suggest simply going with a chart or table in Word or whatever since InDesign isn't used by all that many people, filling the squares with whatever colours you like, and simply inserting the monster info. You could get 4-5 monsters per page which is great for quick reference. If you don't want to worry about colour ink, just do shades of grey instead of shades of green, as in the MM.