Hi,
If you haven't already done your neck and want to darken the fret board, you could try raven oil in brown. The brand I have is Waproo.
You'ld have to mask off around the board carefully, and it can still leak under the tape if you pour it on. But it soaks into the wood well. You can apply several coats if you want. But you would want to seal it in, say with tung oil. You can wet sand the board, in fact the whole neck, with tung oil. Just wipe in down several times well the first 24hrs. If you wet sand it to 2000 grit, it should have a lovely smooth satin finish.