You can save a lot of money on panels by designing the panels as double sided PCB's solid copper on both sides. The corner mounting holes as through holes with the OD of the throughole being close
to the diameter of the screw head. The just specify black soldermask with white ink. and label as needed. Works like a champ. I would recommend? backing off the copper from the board edge someting like
25 mils or so.
As an edge finish you either can use a matte black paint pen or stack up a bunch of them held together with painters tape and masked accordingly and then paint the edges with Krylon flat black spray paint. As long as they are tightly together and you just dust the edges with enough paint to cover (light coats) no paint will get between them.
Alternately you can try a black Sharpie and see how that works but one of my friends says that fades over time.?
Sam Reaves