An alkaline reaction in wood often darkens it the way age does. This is particularly true in nut woods (oak, pecan, walnut, etc.) but works on other woods as well. You can use red devil lye (not draino) in solution, but you have to neutralize it with white vinegar. This raises the grain on the wood, as well as creates odd reactions and tool corrosion. Fuming the wood with ammonia causes the same reaction, plus all reagents completely evaporate on ventilation.
I feel reasonably sure that 100% ammonia is most illegal. Furley dangerous stuff.
If you feel like fuming wood, make an air tight box OUTSIDE of your house or shop (with cross ventilation flaps). Leave a small hole (about 1/2) near the top. Put in the wood supported by the minimum for complete airflow (I like .060 weedeater line or STAINLESS nail supports). Put between 1/2 cup and two cups (depending on wood and box size) of printers ammonia into a plastic or stainless bowl. You may want to use a full face gas mask, unless you love pain. Place in the box below the boards and seal up. With 30 to 50%, this will take about 12 to 24 hours of fume time. Afterwards, remove excess ammonia in bowl (full face mask) and allow to ventilate until the smell is gone. I generally fume completed or semicompleted pieces, as sanding will cut through the effect.