The last bastion of anti-seventh day Sabbath doctrine comes from Colossians 2:16-17 which says: “Therefore no one is to act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day— things which are a mere shadow of what is to come; but the substance belongs to Christ.“
If you take this passage out of its context and use translations which are driven by antinomian doctrine, it is easy to build a case that gentile Christians should not keep the Sabbath or any of Yahveh's Moedim (Appointed Times) listed in Leviticus 23. In fact, this passage may be saying just the opposite.
First off, this is a bad translation of what the passage says in Greek. The phrase "but the substance belongs to Christ" is someone's doctrinally driven best guess as to the meaning of a Greek phrase that is difficult to understand. This passage might be better translated:
"Therefore, don't let anyone judge you in regard to food or drink or in the matter of a festival or new moon or a Sabbath day (these are shades or shadows of what will come) but (be judged instead by) the body
At the time this was written, the judgment of the body of Christ would have been that they needed to obey the Fourth Commandment. In context, this passage begins by saying in Colossians 2:8, "Beware lest anyone take you captive through philosophy and empty (or vane) seduction (or deception), according to the tradition of men, according to the elementary principles of the world, rather than according to Christ."
In other words, reject the ways and wisdom of the world and instead, do as Messiah would do. When verse 16 says "Therefore, don't let anyone judge you...” it refers to those who would take you captive through philosophy and vain seduction according to traditions of men and the principles of the world -- not to the
body of Christ. So it is more likely that this passage is saying that we should only allow the body of Christ
to judge us in these things. When Paul wrote this, it was the practice of the Church to keep the Feasts of Yahveh, including the seventh day Sabbath. It would seem that believers are being told
here not to allow worldly men to judge them for keeping the Feasts!
It is only when you view this passage through the doctrinal lens that holds that keeping the Levitical Feasts and Shabbat are Old Testament Law that does not apply to gentile Christians that you may conclude that it supports the doctrine which colors that interpretation.