If you're like me and wear level your filament (I have a bunch of almost empty spools that I want to keep around so I have a decent color selection), you may find this useful. It lets you put two colors on one spool (or more if you resize the divider and add more than one).

I'd recommend printing just the top centimeter or so to do a test fit before trying to print the whole thing.

There are two versions, sized for spools from Intservo/eSun and Monoprice (these are assembled with screws and are easy to take apart).