The other kind is a droplet, which is created when a block explodes. The droplest match the color of the corresponding block destroyed. Here's a closeup shot:
In other random news, I'm now working at my summer job on campus as an apprentice desktop technician. Also, I was recently met with a couple faculty members at my local community college. They were looking for some one to possibly teach a course in game programming and apparently my boss at my current college gave them my name. They are trying to work out the logistics right now, and if they manage to get the approval, they assured me that I would be the one teaching it. Sounds like a good opportunity so I'm keeping my fingers crossed.