Since the copper is a very thin layer on the PCB, and the substrate is a different color, couldn’t you very easily tweak the code for the two-color ABS to be the default for the PCB material in easel to better show the difference of milled vs. not milled areas? As it stands, the PCB is solid copper and a shallow engraving is a bit tough to see in the visualizer. Brushed copper on tan/gold for instance (which is not a custom option) would be great for this.