He is one of many Celtic Orthodox witnesses, well known for keeping the correct days (and ways) of keeping the Christian Passover. Saint Colman followed in the original Hebrew and Christian Orthodox (Didascalia) Tradition of Saint Columbanus and the Holy Apostle Saint John. The Ephesian church is well known for holding out for the Biblical calendar, and the church of the East overall had used the points in the matter of the great schism.
As is the tradition of the Western Orthodox Church (of the Culdees), not to celebrate on the Calendar of the Pope of Rome, but start our Hebrew year according to the Biblical signs, that lands a few weeks apart from Rome: http://celticorthodoxy.com/2017/05/columbanus-celtic-church-observance-easter-hebrew-biblical/
Also read about the Sabbath in the Orthodox Church (East and West):
Today, February 18th, is the feast (commemoration) day of St Colman (AD 676). Today our family in Northumbria celebrate another great who choose YAHWEH God of Israel rather than the new Roman customs of celebrating Easter. (as was confirmed also the practice of the Bishops of all of Anatolia, ie Polycarp and Polycrates letters and excommunications of Ephesus and all the Bishops of Anatolia for the first several Centuries). After King Oswiu of Northumbria decided the region should follow the new Roman observance of Easter, he retired in humility to the God of Israel to the monastery of Lindisfarne to obey God rather than man.
Rome’s account of the situation:
Bishop Colmán argued the Ionan calculation of Easter on the grounds that it was the practice of St. Columba, founder of their monastic network and a saint of unquestionable holiness, who himself had followed the tradition of St. John the apostle and evangelist.
Wilfrid argued the Roman position on the following grounds (according to Bede’s narrative):
it was the practice in Rome, where the apostles SS. Peter and Paul had “lived, taught, suffered, and are buried”; it was the universal practice of the Church, even as far as Egypt; the customs of the apostle John were particular to the needs of his community and his age and, since then, the Council of Nicaea [incorrect statement, NICEA did not mention Easter, there was a much later comment added, but never has been part of the official canons] had established a different practice;
St. Columba had done the best he could considering his knowledge, and thus his irregular practice is excusable, but the Ionan monks at present did not have the excuse of ignorance; and whatever the case, no one has authority over Peter (and thus his successors, the Bishops of Rome).
Oswiu then asked both sides if they agreed that Peter had been given the keys to the kingdom of heaven by Christ and pronounced to be “the rock” on which the Church would be built, to which they agreed. Oswiu then declared his judgment in favour of the holder of the keys, i.e. the Roman (and Petrine) practice.
The Synod of Whitby established Roman practice as the norm in Northumbria, and thus “brought the Northumbrian church into the mainstream of Roman culture.” The episcopal seat of Northumbria was transferred from Lindisfarne to York. Wilfrid, chief advocate for the Roman position, later became Bishop of Northumbria, while Colmán and the Ionan supporters who did not change their practices withdrew to Iona. Colmán was allowed to take some relics of Aidan, who had been central in establishing Christianity of the Ionan tradition in Northumbria, with him back to Iona. To replace the departing ecclesiastics, Oswiu chose mostly Irishmen who were from the parts of Ireland that kept the Roman Easter (as most of Ireland had done for some time by the 660s).
Today our family in Northumbria celebrate St. Colman the Confessor and third Bishop of Lindisfarne (A.D. 676). Also the festival of ST. ETHELINA, or EUDELM, Virgin whose acts are not recorded.
St. Colman, ST. COLMAN, the third Bishop of Lindisfarne,
and like his predecessors, St. Finan and St. Aidan, was a native of Ireland and a professed monk of the monastery of the great St. Columba in the island of lona. St. Colman was remarkable for the holiness and austerity of his life, his admirable spirit of poverty, and his complete detachment from all the aims and interests of this world. He was also a most zealous pastor, and he and his clergy were held in such veneration, that wherever they went they were welcomed as the messengers of God, their blessing was eagerly sought for, and their instructions heard with devout attention. While St. Colman was Bishop various
questions of discipline, which had long agitated the Church in our island, were brought to a crisis. The chief of these matters of discipline were the day of the Easter festival and
the form of the clerical and monastic tonsure. St. Augustine and his companions had introduced the usages observed in Rome in his time, according to which Easter was calculated by a new and correct cycle adopted by the Popes, not long before the date of the English Mission ; and the form of the tonsure, formerly undetermined, had assumed the shape of ‘a crown around the head. On the other hand, the Irish missioners brought from lona by St. Oswald, like the Welsh already in Britain, followed a computation of Easter which was in fact that prevailing in Rome before the recent correction; and to this they added a second diversity namely, that of keeping the festival on the actual day of the full moon when it happened to be Sunday, contrary to the ecclesiastical rule, which requires that it should never be celebrated until the Sunday after the full moon. This latter mistake caused its upholders to be sometimes called Quartodecimans, though their error was by no means that of those who were con-demned, under the same name, by the Council of Nicaea for keeping Easter with the Jews on the 14th day of the moon, whether Sunday or any other day of the week. The Irish fashion of the tonsure was to shave the entire fore-part of the head from ear to ear, and is supposed to have been brought by St. Patrick from some monastery on the Continent, at a time when there was no uniformity of custom in the matter.
These were clearly mere points of external discipline, in no way touching on the Faith, and the Holy See was content to allow the more correct rule to make its way gradually,
without imposing it as a condition of Communion. But the partisans on both sides were eager for their respective opinions. The Irish pleaded their long custom and the example of St. Columba and other Saints; while their opponents insisted on submission to the usage, which they had found extant both in Rome and France, and stigmatised the contrary practices as schismatical and uncatholic. The practical inconveniences, however, were considerable, and felt particularly in Northumbria, where it had been known to happen that on one and the same day King Oswy and the Bishop were rejoicing in the Easter festival, while Queen Eanfleda and her chaplain from Kent were celebrating Palm Sunday. It was therefore resolved that a conference should be held at Whitby, and the question settled once for all. The chief advocates of the Roman usage were Agilbert, formerly Bishop of the West Saxons, and St. Wilfrid, and the main support of the Irish was St. Colman. After their lengthened arguments had been listened to by King Oswy and his nobles, as well as by the assembled clergy and monks, it was agreed on all hands that St. Peter was of greater
authority and power than St. Columba, and that it was expedient to abandon the practices hitherto observed, and to conform to those generally prevailing in the Church. St. Colman, however, was so deeply attached to the ways in which he had been brought up, and the memory of his saintly predecessors, that he could not bring himself to adopt the change, and chose rather to retire from his See and his Mission. Accordingly, he returned to lona, taking with him a portion of the relics of St. Aidan, and followed by a certain number of English monks from Lindisfarne who adhered to his opinions. After a time they proceeded to Ireland, and established a monastery in the small island of Innis Boffin, on the west coast, where they were joined by other monks, natives of the country. After the first summer the English complained that their Irish brethren had left them to do the work of the harvest, and yet expected to share in the fruits ; and St. Colman, anticipating serious dissensions, thought it prudent to divide the two nationalities. He therefore took the English to the mainland, and settled them in a monastery at Mayo, where they became a numerous community and flourished for a length of time; but before St. Bede wrote they had already given up the old usages which had been the cause of their exile. St. Colman appears to have continued to govern the two communities until he was called to his heavenly reward.
Chapter on the Celtic Church vigorously defending the Easter Calculation of the “14th day of the Month Controversy” in Chapter-Paschal-Controversy-Colman
. From this record it’s gathered a victorious proof of the Celtic calculation.