Colossians 2:16 addresses the specific form of legalism that uses diet, holidays, and sabbath observance as spiritual metrics. Paul says: "Let no man therefore judge you in meat, or in drink." The "let no man" is direct permission to stop internalizing external religious judgment about things that are not binding. The shadow has passed; the substance has come.
Matthew 23:27 is Jesus' most extended and most severe critique of religious performance. He calls the Pharisees whitewashed tombs — beautiful outside, full of dead things inside. The indictment is not that they were insincere. It is that they had separated the exterior presentation from the interior reality that was supposed to generate it. Legalism does not produce the inside from the outside; it conceals the inside behind the outside.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.