Keeping the Sabbath and Colossians 2:16 Colossians 2:16-17, 20-21 says,

16 So let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths, 17 which are a shadow of things to come, but the substance is of Christ.
20 Therefore, if you died with Christ from the basic principles of the world, why, as though living in the world, do you subject yourselves to regulations—21 “Do not touch, do not taste, do not handle,”

The New King James Version. (1982). (Col 2:20–21). Nashville: Thomas Nelson.
That entire portion of the end of Colossians 2 talks about the danger of legalism and seems to discourage keeping things such as the Sabbath (at least keeping them legalistically).  How do Seventh-Day Adventists and other denominations that keep the Sabbath interpret this passage?
"That entire portion of the end of Colossians 2 talks about the danger of legalism and seems to discourage keeping things such as the Sabbath"

Actually, it doesn't talk about that.  In fact it has quite the opposite meaning.

I once used Colossians as an example of exegesis: 
 https://rbutterworth.nfshost.com/Management/examples/exegesis

If you aren't going to read that article itself, at least be aware of the importance of the context in which Paul was writing.

The Colossian Church was isolated from the rest of Christianity.  Most of the people there were Ascetics, who believed that the physical body represented evil while its immortal soul represented good.  That soul must be developed by physical suffering, and so, anyone that enjoys themselves, celebrates, eats good food, etc. is obviously an evil carnal person.

The Ascetics were criticising the Christian converts for their religious practices, and Paul was worried that some of them might feel ashamed of their Christianity and revert back to Greek paganism.  He warns them to "continue in the faith, stable and steadfast, not shifting from the hope of the gospel which you heard".

Here's the section on 2:17:


  2:16-17 resumes the warning about being influenced by the opinions of
  others:
  
  Therefore let no one pass judgement on you in questions of food and
  drink or with regard to a festival or a new moon or a sabbath. These
  are only a shadow [prophetic symbolism] of what is to come; but the
  substance [what casts the shadow, the eventual kingdom of God on
  earth] belongs to Christ.
  
  The original Greek did not use punctuation, but relied more on
  sentence structure. This structure is sometimes lost in translation
  into English (e.g. the original word order is no therefore man you
  let-judge in meat …, the single Greek word being translated into let
  and judge with other words intervening). Punctuation was supplied by
  the translators, who also supplied additional words to make the
  English read more smoothly or clearly. These added words are marked in
  italics in the King James version, which translation (with supplied
  words and punctuation omitted) perhaps provides an even better
  interpretation of this passage:

Therefore
    let
        no man
            judge you
                in meat
             or in drink
             or in respect
                        of an holyday
                     or of the new moon
                     or of the sabbath
                  which are a shadow
                      of things to come
        but the body of Christ

  
  A much more obvious meaning
  immediately becomes apparent: let no one but the body of Christ judge
  you (the body of Christ being the Church). We should not feel bad
  about being condemned by non-Christians for our Christian practices
  such as honouring the symbols of God's promises.
  
  The food and drink, festivals, new moons (monthly sabbaths), and
  (weekly) sabbaths refer to things that the Christian community is
  expected to practice, and not, as some suppose, to unclean foods and
  pagan festivals. The Ascetics were opposed to any form of physical
  pleasure (often including eating meat of any kind), and such holy
  feasts and celebrations (which, except possibly for the Day of
  Atonement, are a time of joy and pleasure to Christians) were a direct
  insult to their beliefs. But these sabbaths and holy festivals are
  symbols to Christians of God's plan for mankind, and must be
  commemorated despite the objections of non-Christians.
  
  In keeping God's sabbaths and festivals, a Christian will be subject
  to criticism from others, and in particular that criticism may often
  be of a very morally superior tone, possibly making the Christian feel
  that he himself might be the one in the wrong.