I've had luck adding a few drops of minwax stain to a tablespoon of 50/50 Tru-Oil/mineral spirits. The end result should be slightly lighter than the stock finish, as is the normal look on unstained work. The Tru -Oil seals the checkering, is tinted slightly already, and at the 50/50 dilution, does not fill in the grooves.
A little age will do the rest.
Jim