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~
Have some paper to push away extruded filament. That's why I always set up the models on the left.
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.