In my business I have several laser engravers for commercial work. I do long production runs only, see Kallenshaan Woods or others for one of a kind jobs. I have found that different types of wood burn differently on the laser. When engraving most (but not all) light woods the recessed area is dark and burned. Some mid-dark and darker woods hardly show the engraving at all, you have to feel the recesses. Maple is a good light wood for engraving; oak, hickory and ash don't work so well. Cherry and Alder are excellant mid-dark woods. Walnut and most darker woods don't show up well.
For most of what we do we use a powder called laser black, it comes from the equipment makers. After we engrave the plaques and boxes, we dust on some laser black, then brush it back off with a dry paint brush, leaving some down in the recessed areas. Then we coat it with a clear lacquer, sealing in the laser black. I tried some laser white and lighter colors, but I don't like the look much.
C