The back color is .6mm thick (3 layers @.20) and then 2 layers of second color.

You can easily scale this and make it thicker, 1mm is pretty much minimum.

Quick Guide to changing filament~

1. Have some paper to push away extruded filament. That's why I always set up the models on the left.
2. When the MK3 jogs after a change it will spit out another inch, so I follow it with paper until it starts to move back down. Doing this has given great, repeatable results.
3. Use a tool like this to help changes→ https://www.printables.com/model/329171-filament-change-tool
4. Have fun!