The symbol is different from that in the first vision. There Zechariah 1:8, they were horses only, with their riders, to go to and fro to enquire; here they are war-chariots with their horses, to execute God’s judgments, each in their turn. In the first vision also, there is not the characteristic fourfold division, which reminds of the four world-empires of Daniel Daniel 2; after which, in both prophets, is the mention of the kingdom of Christ. Even if the grisled horses be the same as the speckled of the first vision, the black horses are wanting there, as well as the succession, in which they go forth. The only resemblance is, that there are horses of divers colors, two of which, red and white, are the same. The symbol of the fourth empire, grizzled, strong, remarkably corresponds with the strength and mingled character of the fourth empire in Daniel.
Related Commentaries of Zechariah 6:2
Zechariah 6:2-3
2 In the first chariot were red horses; and in the second chariot black horses;
3 And in the third chariot white horses; and in the fourth chariot grisled and baya horses.