FACTORY in almost all cases. Most aftermarket grips look like new but cheap wheels on a 17 year old SUV. If you're not from a southern border State, you may not understand.
I have aftermarket grips on my 1911 because I wanted something that looked like OEM GI checkered wood so not sure how to judge that one.
I had an S&W 4516 that came with a gawd-awful set of wrap-around Pacs or something. I found and bought an NOS set of S&W grips.
I "rebuilt" some standard issue Ruger walnut grips for my Blackhawk by stripping them (weren't a matched set), refinishing them, and swapping the eagles for Texas stars. But they're still the same shape.
Hogue over-molds are the ugliest thing you can do to a Blackhawk.
My 22/45RP has aftermarket spalted maple grips. Kind of a blued BBQ 22.
Wood "target" grips are hideous.
Yes, do what you want with your unit but don't expect all to think your three-eyed fat baby is cute.