Seems to me that since three colors would have to be three separate pieces of cord, this defeats some of the purpose of using paracord in the first place... though, yes, if you use appropriate knots you could tie the three pieces end to end.

By the way, a friend reports that there are veteran's groups which are using paracord bracelets and the like as combined physical rehabilitation exercise and fundraiser. I know it goes against the DIY ethic here on Instructables, but that's not a bad cause, so you *might* want to consider buying rather than making.

This is a very well done instructable, and the last step includes information on how to make varients, one of which is a three color bracelet.