Printed with two PETG filaments on a glass bed with hairspray. Printed the black lines (with a custom end code that doesn’t turns off motors) then printed the white over it in a separate gcode (also with custom start with no homing). It even allows me to go with an exact and cut off hairs and blobs before laying the white. The. The two fuse on the same layer so the color isn’t sticking out.
We do this at the lab I work at! It’s really effective and super easy. My boss had me whip up a bunch of signs using this method to designate our different work stations.