The horses' colors do not represent a person or supernatural being. In other parts of the Bible (Zechariah for example), the color of the horses represent the condition of the time period or place. White: Peace ; Red: Bloodshed ; Black: Famine/distress ; Green/Pale: Death.
In Rev 6, these horses represent judgments on Pagan Rome, followed by persecution and national upheaval.
The White Horse in Rev 6 represents a conquest of Christianity in Pagan Rome. That conquest will be completed by Jesus Christ on a white horse after his return.
Reply from Watchman Bob:
Steve, Your interpretation is very subjective, not based on correct exegesis of Scripture - allegorizing away the clear "end of the world" (Mat 24:3) implications of the book of Revelation.
It also ignores the fact that end-times Bible prophecies are invariably partially and typically fulfilled one or more times before their final fulfillment at the "end of the world." For example, Antiochus Epiphanes violating his treaty with the leaders of Israel by desecrating the Temple and pursuing the Jews into the wilderness, where his army was defeated in 167 BCE by the Maccabees, led by Judas Maccabee (a type of the Messiah), and the kingdom restored to Israel, was a partial fulfillment of Dan 9:27, which, according to Mat 24:15-31, 2 The 2:4, Rev 12:13-16; 19:11-21, Zech 12:9; Eze 36:28 and many other passages of Scripture will be completely fulfilled at the end of the age.
So, yes, the destruction of Rome was a partial, typical fulfillment of the Rev 6 prophecy, but did not come close to the ultimate fulfillment at the "end of the age."