What needs to be emphasized here is that when Christ died on the Cross and declared "It is finished", it was as much a reference to the end of the Old Covenant as it was to his perfect redemptive work on the Cross.
The Old Covenant did not end at the cross which is why Hebrews 8:13 says it was "ready to vanish away". This was written long after the cross. "It is finished" refers to Messiah's work of redemption.
All feasts, festivals, holy days, new moons, and sabbaths were a part of the Old Covenant given to Israel. Therefore none of of them are mentioned in Acts 15. And this is critical.
I assume you are referring to the fact that only four specific laws were given to the Gentile converts? If so, then they are permitted to break all Ten Commandments (with the possible exception of the first). Oh, but you would say nine of those ten are commanded elsewhere in the NT. Correct, but that invalidates your argument here about them not being mentioned in Acts 15. So it is not as critical as you think. Actually, those for prohibitions were given to the Gentile converts as a starting point to foster fellowship with Jewish believers. However, Acts 15:21 tells us why they were given only those four; "For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day." The new converts would eventually learn the rest of Moses as they heard him taught every Sabbath in the synagogues. There were no Sunday services at this point in history. Going to a synagogue was the only way to hear the Word of YHWH read.
So you can interpret Colossians 2 any way you want, but none of those observance are for the Church. Since Christ our Passover was already sacrificed for us, the only feast for Christians is the Memorial Feast of the Lord's Supper on the Lord's Day (the first day of the week).
It is interesting that you should mention "Christ our Passover" being sacrificed for us. What did Paul say after that?
1Co 5:7-8 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us: Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
What feast? He was referring to the Feast of Unleavened Bread which started a few hours after the Passover lambs were sacrificed. He certainly was NOT referring to the Lord's Supper which began being kept on the first day of the week long after Paul died.
However, if you wish to observe the Old Covenant, then you must observe all of it, and since that is an impossibility, you know you should stick with the New Covenant and New Testament truth for the Church.
I do not observe the OC. I am a NC believer who believes YHWH's words when He says through Jeremiah that "TORAH" would be written on hearts and minds of NC believers (Jeremiah 31:33);
But this shall be the covenant that I will make with the house of Israel; After those days, saith YHWH, I will put my law (Hebrew - TORAH) in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
All Jews knew exactly what He meant. Yes, I will stick to the NC and the New Testament truth as revealed in Scripture, but not as distorted from pulpits.
