I’m delving into a new area and wanted to see what ideas or things you’ve tried that have worked.
I have a piece where I’ve engraved a design, lacquered over it and have gone on to finish up most everything else. Now that I’m looking at it, I’m finding that I’m wanting to add some color to the engrave to make it pop a bit more. Has anyone been able to put color into a previous engraving and been able to wipe, sand, clean it off the surrounding area successfully?
I have used a rapidograph to ink an engraving, the fine tip allowing exact placement and control… But slow as Christmas.
You might try a sharpie on a scrap and see if alcohol or another solvent would let you remove it without attacking the lacquer, or maybe reapply the finish afterward. 
…or practice old school gasket making and apply a mask and rub an impression of the engrave on it and surgically cut it off the engrave with an exacto knife and spray away.
probably too detailed for me to get with an exacto knife. BUT since I still have the file, I might be able to laser it out of masking, lay over top and spray away.
I have no issues with refinishing the piece again, I am using spray lacquer on this particular piece, so that would be easy to accomplish.
Sharpie is my go to for coloring anything already finished. It can be removed with a damp magic eraser, but if you have a gloosy finish, you’ll want to add a top coat when you’re done…it does dull the finish just a bit. 
what color would you suggest putting into Walnut? I’m leaning towards white since it would be a high contrast against the dark wood color, but I’m worried that it will look too…stark of a difference?
Black could be good, but I’m not sure that will actually stand out from the wood color.
I almost want an almost maroon, or wine Red sort of color, and not sure if Sharpie comes in that color.
Yes, it’s got some deep reds, and they would look very burgundy colored over the walnut…hang on…
That’s one of the pens in a package of 36 or so that you can get at any Office Depot.
yeah…I like that. I’ll be near an office depot tonight!
Oh good lord there’s a 36 pack of Sharpies? Are they all different colors? This is good news for this Sharpie-holic… and I thought I was in heaven after learning I can use my hardware store discount to get black Sharpies by the case!! 
Yup! I’m a pusher. 
Oh… my… God… 115 pack. 
We dont have an OD here and Staples doesn’t have such wondrous goodies.
https://www.officedepot.com/a/products/379659/Sharpie-Ultimate-Pack-Assorted-Colored-Pack/
OMG! Twin Tips!
(Now why’d you have to show me that…they’re out of stock!)
one of the benefits of working at an architecture firm… colored pens and pencils by the bushel load in the supply room…
I really like the Sharpie Paint Pens. Have used them a lot on 3d printed items.You PROBABLY need to seal your engraved item if it is at all porous (draft board, plywood, hardwood).
They come in Extra Fine, Fine, Medium and Wide.
https://www.amazon.com/gp/product/B005QEZAFA/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
@Jules, your husband has it so easy this time of year with respect to Christmas presents for you. Seems like packs of colored markers, and assorted scraps of wood and plastic is all it takes. I hope you use that stuff and make him something really nice!
Totally, totally true!
I bought the 30+ pack and thought I was rocking it…
They are so easy, quick dry, color is vibrant and they are cheap.
Oh, squee … those Sharpie Paint Pens look like a lot of fun.
(you guys are a bad influence … my Amazon wish list increases exponentially whenever I visit the forum)