Like everything else in Scripture, the context has to be examined. In the early church, as you probably know, most converts were Jewish, and there was a constant tension and disagreement among them as to how much, if any, of the old testament law had to be observed. This comes up for discussion in Romans, Galatians and other passages of Scripture. This passage in Colossians is talking about the same thing. It mentions in verse 14 “having canceled the bond which stood against us with its legal demands” (a reference to the OT law) and then verse 16 mentions food, drink and festivals, all part of the OT ceremonial law. It says in verse 17, “These are only a shadow of what is to come; but the substance belongs to Christ.” In other words, all the OT ceremonial observances pointed to Christ, who is the saving reality. So it doesn’t matter if a Christian observes them or not (and Christians at that time shouldn’t judge others if they do or don’t observe the OT cermonies) because they have no power to save. Hebrews 9 and 10 discusses this also. So this passage can’t be used to deny the idea of absolute truth because the passage is actually confirming that absolute, ultimate truth is Jesus Christ and everything else is a shadow of that truth.
“Follow the pattern of sound words which you have heard from me, in the faith and love which are in Christ Jesus; guard the truth that has been entrusted to you by the Holy Spirit who dwells within us.” 2 Tim. 1:13
“For the time is coming when people will not endure sound teaching, but having itching ears they will accumulate for themselves teachers to suit their own likings, and will turn away from listening to the truth and wander into myths.” 2 Tim 3:4-5
“Take heed to yourself and to your teaching: hold to that, for by so doing you will save both yourself and your hearers.” 1 Tim 4:16