In the first chariot are red horses, and in the second chariot brown horses,

In the first war-carriage were red horses; and in the second, black horses;

In quadriga prima equi rufi, et in quadriga secunda equi nigri,

The symbol is different from that in the first vision. There Zac 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.

In the first chariot were red horses - The empire of the Chaldeans, which overthrew the empire of the Assyrians.
The second chariot black horses - The empire of the Persians founded by Cyrus, which destroyed the empire of the Chaldeans.

In the first chariot [were] (c) red horses; and in the second chariot (d) black horses;
(c) Which signifies the great cruelty and persecution that the Church had endured under different enemies.
(d) Signifying that they had endured great afflictions under the Babylonians.

In the first chariot were red horses,.... If these are to be understood of the apostles of Christ, and ministers of the Gospel, they may be compared to "horses", for bearing the name of Christ, and drawing the chariot of the Gospel; for their strength to labour in the word and doctrine; for their courage in the cause of Christ; and for their swiftness in doing his work; and to "red" ones, for their flaming zeal for the honour of the Redeemer, and their bloody sufferings for his sake: and if of angels, they may be compared to "horses", because strong and swift to do the will of God; and to "red" ones, because they are the executioners of his wrath and vengeance on wicked men: but if by "the chariots" are meant the monarchies, then by these "red horses" must be designed the Babylonians and Chaldeans, so called because their soldiers were clothed in red, and their chariots were like flaming torches; and they were sanguinary, cruel, and bloody in their tempers, and in their actions to the Jews; and were signified by Nebuchadnezzar's head of gold in his image; see Nahum 2:3,
and in the second chariot black horses; which, applied to the apostles and ministers of the Gospel, may denote their mean and abject appearance outwardly, and their knowledge in the mysteries of grace, which are dark and obscure to others; and, if understood of angels, is applicable to them, when messengers of ill tidings, or executioners of judgment: but if the monarchies are meant, which seems best, the Medes and Persians are intended; and their "black" colour is expressive of the sorrowful estate of the Jews under them, especially in the time of Haman, as Jarchi and Kimchi observe: black horses were reckoned strong, well made, and fit for labour; and the Ethiopians and Moors chose to have their horses they used in war all of this colour, to strike the greater horror and terror into their enemies; and to see black horses in a dream was accounted a bad omen (s). The Medes and Persians were a strong and warlike people, and were very terrible to their enemies, under Cyrus; and very troublesome and distressing to the Jews, under Cambyses and Ahasuerus.
(s) Vid. Bochart. Hierozoic. par. 1. l. 2. c. 7. col. 106, 107.

red--implying carnage.
black--representing sorrow; also famine (Revelation 6:5-6; compare Zac 1:8).

Red horses - Perhaps denoting bloody times, Revelation 6:4. Black horses - Perhaps a time of mortality, and wasting diseases, Revelation 6:5.