Just out of curiosity..........why would Paul being telling these folks Previous pagans) these things?
They were being ostracized by their pagan neighbors for doing exactly what you folks think Paul was telling them not to do. Think! They never did these things before so why would Paul even mention them? What this verse really teaches is....."Don't let these pagan gnostics JUDGE youfor HOW you are keeping YAHWEH'S holy days". In other words.....it's an affirmation that these folks were actually observing Yahweh's ordained dietary restrictions and his ordained Sabbaths. They had been taught these things by Epaphras [1:7][4:12][Philemon 23].
By cautioning the Colossian Christian converts to not let others judge them how they observed these things is proof they were indeed observing them! Paul wasn't questioning them in whether or not they should be kept. The obvious implication is.....they were keeping them.....and....Paul did not tell them to desist!
Because their were Judiaziers (ravenous wolves) following him around telling the new Christians they had to follow the OT law. He warns about them several places in the NT. Boy, kinda like the point some are trying to impose on this thread. Why would he say these things were just a "shadow of the things to come" but that the substance "belongs to Christ" if he was defending them? That makes no sense and would completely contradict Romans 14.