One technical way to get multi-color is sometimes expensive and still limiting - that is to get a dual-extruder, where two colors can be loaded and printed during one print cycle. Our school tech club has a FlashForge dual extruder, and while it's cool, it's still limiting - allowing exactly two colors.
Another way to get multi-color #3DPrinted objects is to design models which are multi-part so that each part can be made in different colors and then connected. This is my preferred method so far - but it is truly hard to design in 3D Modeling software with this in mind.
Of course there are much more expensive printers which achieve not only multiple colors, but even full-spectrum color, like your desktop paper printer does. But with the types of 3D printers that most of us have, I found another, more crafty (some might call it fake) way to achieve multi-color - that is, to print your objects using white filament and then use Sharpie (tm) markers to color the models any way you want. What I like best about this method, is that it requires some good old-fashioned arts and crafts action - drawing with your hands (imagine that!).
I've experimented a bit with this, and so far it works pretty well. Included in this post is a video (quick time-lapse) of me coloring a miniature version of my custom designed Minecraft (tm) TNT block. I found that using Sharpie's for even minor highlights really makes some models look significantly better. When I print that same TNT block in pure red - it's hard to see the letters or the other details, like the fuse on top, which I can now color in black.
My experiment with the Minecraft (tm) sword shown in the images in this post was circularly inspired by my friend Alice Keeler's post where she suggests using spreadsheets as a pixel art creator - and she showed an image of a pixel-art Minecraft sword. I used that design as a guide to try coloring my own #3DPrinted Minecraft Sword... Not too shabby (ok, a little shabby).
|The before (white) and after Minecraft(tm) Sword!|