Just for the record I use boiled linseed oil. Just a smidge in a kitchen towel, tap a dot of it on every 'fret square' along the fingerboard, rub it in then immediately wipe it all off with a clean kitchen towel.
Makes the grain pop and look amazing!
I got this tip off Talkbass from Roger Sadowski himself. He does exactly this to all his builds with rosewood fingerboards.