The vision during the night follows a standard pattern:
an introductory statement,
a description of the vision,
the prophet’s request for an interpretation, and
an angelic explanation.
The myrtle trees were likely in the wooded Kidron Valley outside Jerusalem. The Lord had symbolically returned to the edge of the city. He had not yet entered Jerusalem because the temple was still being rebuilt.
The colors of the red, brown, and white horses are not important to this vision’s meaning. These angelic riders patrolled the earth (Zechariah 1:10), showing God’s ongoing concern for Jerusalem.