I'm working on a Singer 99k at the moment with the same gold flecks showing in the shellac.
This machine had a lot of areas where the shellac was alligatoring and lifting off the base coat. I think the gold flecks are tiny air bubbles under the shellac where the shellac is separated from the base coat and the gold color is the true color of the shellac finish. I'll rub the machine down again today with just alcohol and linseed oil before I try adding any more shellac.
One great thing about this method is problems are easy to catch before you go too far and shellac is a very forgiving finish to work with.
I'm working on this machine for my 10 year old daughter to bring to her 4H meetings. I want it to be pretty so she can be proud to show it off when she's there.
Rodney