Staining

The one area I'm most eager to see continued development in post-printing grip finishing is staining the wood composite grips.  While the grips feel like wood in your hand, you won't without lots of work soon mistake them for a beautiful piece of black walnut.   The challenge in working with stain on the grips is liquid does not readily soak into the grip as it would if it was a solid piece of wood.    

There are some YouTube video of cos-players finishing their 3d-printed pieces with various paints and stains you might want to explore.  However Craig B, who shoots an LP-10e has had some success he is happy to share.  Below is what he wrote and a picture of his LP10e grip.

The stain took to the material well.
Search the web for alcohol based wood stains, you can find a lot of info. 
I discovered from various forums on the web that alcohol based stains are very flexible for blending colors for gunstock work, and if you are not happy with the color you applied you can wet a rag with denatured alcohol and wipe away the stain you applied and get vary close to the bare wood.
If the color is to dark, you can wipe with alcohol to lighten it up too.
Often I apply  a coat of walnut or dark brown and then wipe using the same rag some blood red, it can create really nice tones on walnut stocks.
These stains offer lots of forgiving flexibility compared to oil based stains to get the “just right” color and contrast you want on a gunstock.
Here are the stains I used:
http://www.woodcraft.com/category/SU106-13/stains/behlen.aspx
 
You can also blend this leather dye to get similar results:
http://www.amazon.com/Fiebings-50-2046-BU-P-Leather-Dye/dp/B00XOXGUM2
I use the black dye to cover stippled areas on walnut stocks, it works very well.
I have used the brown colors too with blood red behlen stains.