Unfortunately, in a modern engine it is very difficult - if not impossible - to tune the engine by reading the plugs. If it's covered with soot, it's really rich. If it's
oil fouled, it's probable not firing. That sort of thing. Otherwise, you need a wide band sensor to do a really good job of tuning.
If you think it''s a bit rich, I'd leave it there. Better to be a bit (not a bunch) rich than a bit lean.