Lest anyone get the wrong idea about “Ordinary” time, it doesn’t mean normal, customary, regular, or anything like that. It means the days, excluding the seasons of Advent, Christmas, Lent, Easter, etc., are counted, in a certain order.
Remember that ordinal numbers refer to those used for counting (1, 2, 3, 4…)
In that sense, Ordinary time is the same kind of idea as “Sundays after Pentecost”. The beginning and ending points are just different.
The part about wearing green is the same…