MakerBot Discover: Dual Extrusion 3D Modeling with 123D design at this link.
https://www.youtube.com/watch?v=_1giymE4iXI

2 colors: with DaVinci 2.0, you load two separate STL files into the XYZware print space, then right-click on images and tell it which extruder for each file. Have to make sure you have no overlap or unwanted gaps between, and that Autoposition under Settings is unchecked before importing STLs.

One more thing: Highly recommend adding Raft for anything larger than 1 cm square base; this mostly eliminates warping on things I've tried so far.

well, in Slic3r you can choose which part of the model should be printed with which extruder.
Example:
           Perimeter extruder:           1
           Infill extruder:                  2
           Support material extruder: 1

The number specifies which extruder (1 or 2) should be used for that task. You can read more here: http://manual.slic3r.org/expert-mode/multiple-extruders

As for the simpfy3d you should read this: http://www.simplify3d.com/support/tutor … extruders/

But I think that if you want a specific part of the model to be a specific color (lets say you only want your bottom left corner to be red ), than you'd have to change the G-code, rather than just shift some setting around.
You could try Slic3r's feature to combine multiple STL files into a multi-material AMF file but I cannot atm, being on the davinci 1.0. You basically split the original design into the separate parts within the 3d modeling program, and export each part as STL. You can read more in the above slic3r link.

In G-code editor, I can see which extruder is being used to print which layer (I only have 1 extruder, so it always says E0)
So if I wanted a model to be, half blue and half red (from bottom up), than I would just change the E command in G-code from E0 to E1.

Like I've said, I would if I could... but I cant. So I could be wrong.

I use simplify3D and usually just print .stl files from Thingiverse. If I have one monolithic object, how do I tell it to print one portion of it in blue and the rest in red? Can I only indicate that it is to print one entire object in blue and another entire object in red in the same print job? If so that doesn't sound very useful.

Please be patient, I am trying to understand the capabilities of dual extrusion printing.

Thanks

dual extruders will give you an option to to print in dual color, but that is just a beginning. It all depends on which type/brand of extruder are you going for (e3d, pico by E3 innovations, another extruder from xyz, etc).
With e3d/pico you'll be able to print in different materials (PLA, Ninjaflex, PVA, Taulman nylon, etc), use a different material for support (like HIPS) which can be dissolved with D-Limonene (citrus solvent), and also print at higher temperatures than with stock hot end. So if you can, my suggestion to you is that you upgrade.

About two colored models: You put two different colors in your hot end and than, in your software, you set which one should print what (you tell the software which part of the model should be printed with which extruder), so it doesn't matter if the models from thingivere are not in two colors.

hope it helps

Are there many models on places like Thingiverse that have 2 colors? Are there many free 3D design packages that would allow me to make my own? How hard is it to make a model that has multiple colors?

TIA

STeven