Sanding and Filing
The other side of puttying grips up is sanding and filing them down. 3D-printed grips sand and file like wood, but with a couple of important differences. First, if you go at them with a high-speed tool, like a Dremel, be very careful. The heat generated can deform and even outright melt the grip if you are not careful. Use a small rough drum and keep the speed slow. Secondly, don't forget that the grips are not solid, but a 1.5 mm thick shell over a sparse honeycomb matrix. If your work takes you through the shell don't worry. The material is so stiff you won't damage the grip's structural integrity and you can easily putty the hole back up.
Something else to consider is the over-all finish. The PLA grips come off the printer rather shiny. Seemingly even more so as exacerbated by the lighting in my shop. I find that finish, particularly with the black PLA, a bit harsh in that light. That is one of the reasons I choose the pewter PLA when asked for my preference. Nothing is wrong with that finish, it just isn't my favorite. You'll discover once you start sanding that you can take the grip from shiny to matte very quickly with some sandpaper. This quick work also improves the feel in your hand.
I have to admit I struggle a bit in delivering grips with a uniform finish. If I do nothing to them after they come off the printer they are maximally shiny, smooth and look great. But they also inevitably have a few stringy parts of material that need to get clipped, filed, or snipped off. This post-printing handwork is particularly evident in the places where the grip has overhangs, like the parts above your hand and middle finger. Grips are printed from the bottom up, one layer at a time with a tiny thread of extruded material. That material bonds to the layer immediately below it. These overhanging areas require a tower-like support that is cut away after printing. This tower gives those overhanging layers something to sit on until the layers above add their own stability. Clearing away those support towers results in a few areas being matte while the rest remains shiny.
Below is the same grip. The first is fresh off the printer and the second is after a couple minutes of sandpaper work.
It doesn't matter if you're still trying to find the black, or have been a High Master for so long you look at a 9 as a tragic mistake, you're probably never going to be done working on your grips.