Colossians is dealing with the festivals of the Jews who had now become apostates by not keeping up with new light. LOL The passage is completely relevant, in Paul's opinion if someone wanted to continue to do them or not due them it was no one's business.
What's interesting is that Paul was accused of vacillating and being a backslider in regards issues of traditions of Judaism by more militant Christians. He tries to defend himself as "being all things ...so as to save some". (Funny how Timothy, an adult man, is the one getting his ding-a-ling cut so Paul could pretend to be keeping the Law and avoid getting beat up). Is it OK to give a misleading impression if it gets converts or saves your skin???...but that's another topic.
Something to think about is those festivals of the Jews, what they were and how they originated. Most of the festivals are seasonal celebrations to ensure crop and animal breeding success from the gods (and eventually Yahweh exclusively). Apotropaic magic is the very theme of the festivals. Warding off the punishment and ensuring the blessings by ritual and symbolism. It's been long suggested the Passover was originally an indigenous festival (or combination of two) to have the rains pause. Of scholarly interest is how the people of Caanan understood Baal being swallowed by Mot seasonally to have Baal and the rains return when needed. The bones of the Passover sacrifice were not to be broken for that reason. It appears that the festival was revamped/rehabilitated as a commemoration of an expulsion from Egypt (Hyksos??) under Josiah for political reasons. Anyway, the festivals in the OT, if anything, illustrate the need people have for seasonally celebrating life and renewal. They also illustrate the syncretic nature of religion.