Heres something we've offered a few times, and it was well received...infused Kydex. This isn't a coating like paint, etc...it actually becomes part of the surface of the Kydex and will never peel, wear off, etc. The only way to remove it is by sanding/gouging it off and it holds up well to that too. I've tested it where I've sanded it with 200 grit sandpaper with heavy pressure for a full minute and while it lightened the design slightly, it was still 90% there. Thats far more abuse than your average sheath will encounter through its life.
Most makers only offer repeating textures life camouflage, etc. That's because those are much easier to make sheaths with as you don't need to line the design up. With something like an oni face, dragon, etc you need to think about the shape of the finished sheath, and get all measurements correct before even starting to mold the Kydex to the knife. If you don't, the design will be cut off when making the sheath. We offer both designs tailored to the sheath, and also textures/repeating patterns like camouflage
The pros:
the print becomes part of the plastics surface and holds up very well
adds a wide variety of designs to the sheath
since we do it in-house we only charge $10 extra for this service...which is much cheaper than most makers who need to buy already printed designs...which are pricey...and mark up the price from there, often charging $25-50 extra pers sheath, sometimes more
The cons:
to get vibrant colors you need to start with white Kydex. If you printed on back, it would barely be visible. You can however print black on any color. For example black on fluorescent green, as shown in some of the photos. The inside of the sheath is the color of the Kydex, and so are the edges of the sheath where its been sanded to smooth down the rough edges after shaping the sheath.
Kydex sheaths normally have a haircell texture on the exterior. The infusion process will flatten this texture out a bit, creating a smoother texture. Since its been flattened slightly, the Kydex can feel slightly thinner than uninfused Kydex but no material has been removed, so it retains 100% of the original Kydex strength.
Raises the price a bit since there are extra steps involved.