I printed my own waterslide decal on my laser printer using decal paper from http://www.water-decals.com/decal_paper.html . This neck is finished in Warmoth's satin vintage tint nitro. Here's a picture of it:
In my case I designed the decal in photoshop and then printed it on my laser printer with decal paper from
DecalPaper.com - Decals - Waterslide decal paper or inkjet,laser printers Alps & copiers . Then I followed these directions that I got off of here (I modified them slightly so this is my modified version):
First thing is to level the existing finish in the decal area with some fine 800 grit sandpaper - VERY LIGHTLY.
Clean it well, no dust, no nothin' - used a tack cloth
Clean it again with naphtha to degrease it
Apply the decal (waterslide).
Use solvaset decal setting solution to melt the decal into the finish
Let the decal dry at least an hour, if not more.
Mask off the fingerboard and just under the face of the headstock
Apply very sparingly CLEAR shellac over the decal area. Its ok to get the shellac on the lacquered areas. I used Zinnser Bullseye Sealcoat because it is completely wax free. I sprayed it out of a disposable aerosal bottle
Apply another coat of clear shellac over the decal area. The shellac will be a barrier between the lacquer and decal, and also, its alcohol solvent will take any remaining water out of the decal membrane - VERY important to do, or you can cloud/lift/bubble the decal.
Apply a light coat of lacquer, let it dry an hour or more (I used ColorTone clear satin nitro from Stewmac.com for this and all subsequent steps).
Apply another, let it dry an hour or more
Apply a medium wet coat of lacquer, dry an hour or more.
Apply a medium wet coat of lacquer, dry a day.
Use 600 or 800 grit paper to level out the finish over the decal only. Do not level (yet) over the other areas.
Two more medium wet coats, dry a day.... level again, just over the decal area.
One more medium wet coat - and inspect to see that the decal has "leveled" into the finish, after that coat is allowed to dry for an hour.
If it has sunk in, one more wet coat, let dry two days or more.
Between coats I would wipe it down with a tack cloth and after sanding I'd wipe down with the naptha.
By doing this the decal is completely flush with the face of the headstock - it looks just like a factory fender job. It took a couple weeks to get it done but IMO it was worth it - it looks sooo much better than a sticker like they include with the neck. Obviously this would only work if you have a finish on your neck. The solvaset solution does a very good job of "melting" the decal into the wood though even if you have a raw neck. It's used commonly in the model building community - http://www.houseofhobbies.com/sodeseso.html .
If you wanted to do color many larger copy shops have color lasers available that you could print from. Only problem is that you need to start with the printer cold so that it doesn't the transfer paper so you'd want to arrange it with them and show up first thing in the morning to run your print job. Keep in mind that printers don't PRINT white - white is a lack of color so you don't want white in your design.