Though it's possible currently by manipulating the GCode and inserting a @pause statement, I'd love for simple GUI support to change filament colors mid-print, similar to the interface the process settings can change at a layer height. I'd love it if it event prompted me for 'Insert green filament now' or something similar in case I zone out, similar to the way a CNC will ask for a specific bit.
Here's more info on single extrude multi-filament printing: http://meow.noopkat.com/3d-printing-in- ... -extruder/