What is the significance of red horses?
Rashi: They drove the chariot of Bavel, which is red - "Ant Hu Roshah Di Dahava" (Daniel 2:38; gold is reddish).
Malbim: Malchus Yavan went first. They were prepared to spill much blood, like in the first chariot, he saw a man riding on a red horse (1:8).
What is the significance of black horses?
Rashi: They drove the chariot of Madai, which blackened Yisrael's faces in the days of Haman.
Malbim: This represents Malchus Edom, which was after Yavan. Also they were prepared to spill much blood. Also black is a color of blood - it was red, but it was stricken [and turned black - Chulin 47b]. Black also signifies the dark Galus and long night of Yisrael in Galus Romi.
Above it says that the second horses were "Serukim" (1:8). Here it says "Shechorim"?
Radak #1: Here they appeared black, for they blackened Yisrael's faces in the days of Haman.
Radak #2: They are two nations (Paras and Madai), even though they are one kingdom. These colors are based on the color of the garments of people of these kingdoms. One nation wore Serukim, and the other wore black.
