Flooring Tile - Hiding a screwhead in bath surround panel

Hi, I want to disguise a couple of flat head screws I'm fastening in a bath surround panel. [The screws are to secure the somewhat warped panel (it's about 28 years old) against the substrate, which looks like drywall. The screws will fasten to a framing 2X4 behind the drywall. I'm putting the screws about 2 or 3 inches from the edge of the panel on only one side because the other side is still fairly secure. The bath probably should have new surround panels, but until then, this will hopefully do.] The screws will be tightened to just below the surface of the panel. I don't know what kind of bath surround panel it is--cultured marble, solid surface, acrylic, cultured onyx, quartz composite, or another type. (I wanted to include, with this question, a couple of photos of the surround panel, to help identify it, but under Posting Rules, it reads that I 'may not' post attachments.) I read on this website one way to fix a hole in ceramic tile is, take epoxy, mix acrylic paint (to match the tile), and then fill in the hole with the mixture using a putty knife. But is epoxy OK for any of the kinds of panels that I listed above? Or are there any other types of fillers I could use? Maybe unsanded grout? Or, is there another way to disguise?
Thank you,
Mark :thinker: