You've probably noticed the colors changing periodically up on the altar paraments, sanctuary banners, and Pastor Rebecca's vestments as we progress through each church year, especially around the time of major church holidays.
From the Christian worship-music reference site Hymnary.org:
"We have entered "Ordinary Time."
Ordinary Time" — "the green season" — may almost seem like a letdown after celebrating the great themes of Advent, Christmas, Lent, and Easter, but it is in "ordinary time," after all, that we live most of our lives. This season covers the time between Epiphany and Ash Wednesday and between Pentecost and Advent. The liturgical color is green.
Ordinary Time includes several specially designated Sundays with their own focus and colors, including Trinity (the Sunday after Pentecost) which is dedicated to the Christian belief in the Trinity and which falls on the Sunday following Pentecost each year.
If you're interested in finding out more about the various "seasons" of the Lutheran church calendar, Wikipedia has a pretty decent write-up: