Ah, Pathfinder-era earth PADDs are a subject of great interest! Those episodes made extensive use of all sorts of interesting PADDs, but none of the TNG radiused rectangles that I can recall. I believe the clear PADDs replicated by @kertratz were first seen there, actually.
And there were also versions of the curvy VOY PADDs but with a red paint scheme .
(As a aside, PADDs in the normal non-engineering shape of the day but painted in red have historically been associated with earth Starfleet facilities and other special circumstnaces, with the first rounded-rectangle red PADDs being seen at Starfleet Academy in “The First Duty,” and occasionally recycled later.)
(from the TNG 365 book, p511)
Here is a standard VOY PADD on earth, but in red, a color I don’t think we ever see on Voyager itself.
“Inside Man” 28:15 (here, again, on earth)
They did FWIW use the brushed metal vinyl sticker stuff for the largest leftmost button.
I think I am with Ethan on this. I’ve never seen the art department use this technique (since I haven’t really studied late-season DS9 or ENT props very closely), but it’s very cool. There may also have been colored gels in there like in the TNG translites as well, but that seems like a lot of work. There is always also the possibility of screen printing, but since they had the ability to make the positive transparencies (a normal necessary step in the screen printing process), they might just as well have used those and skipped a step unless they were making a large number of the prop in question.
But now that I look at the other images of that PADD, I’m not so sure.
It’s possible, but I doubt they were cutting gels for all those tiny bits on such an incidental prop. The question for me is where this colored anodizing effect (like you used to see on old Apple iPods mini) is coming from. Perhaps this was some kind of sign-making technology in use at the time, like a brushed metal vinyl that could be printed on with inkjet or something? Or I suppose it could be some kind of screen-printed translucent colored ink.
I’m really curious about this now!