That’s actually really fascinating. Color abnormalities and partial leucistic/piebald traits do occasionally show up in wild bluegill, but most probably never survive long enough to become noticeable because they stand out to predators. In a heavily fed pond with reduced predation pressure, unusual genetics probably have a much better chance of making it to adulthood. Could also simply be an unusually strong expression of their iridescent breeding coloration, but the “bright shiny blue patches” definitely sounds interesting enough that I’d love to see photos if your friend manages to catch one.