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.
If you increase your z-hop on retraction enough, you can make these colors more than one layer and still avoid them with subsequent colors, which helps if you’ve got a light color that needs a couple layers to be fully opaque, like a yellow.