I am a hands on learner so I wanted sample trays that I could physically hold and look at to decide which infill to use. I saw similar designs already out there but I wasn't completely satisfied with them so I designed my own.
The cube's designed height is 25mm tall but actual height is 20mm. To do this, first I chose the infill type and percent I wanted. I then input the gcode into ColorPrint (http://prusaprinters.org/colorprint-is-out) and chose to change color at 20.150mm. Finally I printed the cube and when it got the the color change part, and the cube was 20mm tall, I would just cancel the print and that would leave the infill exposed.
I am not sure if this software works for everyone so another way to do this would just be cancel the print when it gets to 80% and the cubes should be roughly 20mm tall too.
The trays total heaight is 22mm tall (3mm of which is the lettering). I also used ColorPrint (http://prusaprinters.org/colorprint-is-out) to change the colors of the lettering. I did the color change at 19.150 so the entire lettering were a different color. This is an unnecessary step but I think it looks much better. I designed the lettering to be the same height as the cubes so everything is flush on top.