Best Permanent Marker for Grey Pro

hi, I am currently trying to find the best permanent marker for Grey Pro. I printed some parts with cut out sections that I am trying to make stand out more by using a permanent marker. So far I have tried shop paint pens and sharpie, both of which did not stay in the cutouts following sanding.

Has anyone ever tried this before? What did you find?

Thanks!

Wait, as you hoping the resin will absorb the marker below the sanding level?

I need the marker to essentially dye these areas, typically on delrin or pvc paint markers and wet sanding work perfectly, but Grey Pro does not retain the marker as well…

I doubt anything will work, as this is methacrylate, but you can try with a nylon dye and see if that does the trick.