Dave from Pygmy Boats called me and said he didn't think it was mold. He said that it was either something in the glue that was showing through with the epoxy coating on it, or a defect in the plywood itself that only showed up under the epoxy. He said my options are: replacing the shear panels, or living with it. There is no way to sand the area out. They would send me new panels but the work to take the panels off and re-glue them would be horrendous and the new panels might be darker or lighter than the current ones and might stand out more.
Does anyone out there have any better suggestions?

Charles Robinson