Of the Four Horsemen of the Apocalypse, what is the color of Famine's horse?

The black horse is the symbol of famine.

The Four Horsemen of the Apocalypse are described in the New Testament of the Bible, called the Book of Revelation of Jesus Christ to John the Apostle, at 6:1-8. The Four Horsemen were symbolic descriptions of the events which depicted the end of time.

The white horse is described in Revelation 6:2, "I looked, and there before me was a white horse! Its rider held a bow, and he was given a crown, and he rode out as a conqueror bent on conquest." “The Antichrist is seen riding a white war-horse, and with bow in hand, but with no arrow fitted to it. The symbol suggests bloodless victories.”

The red horse is described in Revelation 6:4, "Then another horse came out, a fiery red one. Its rider was given the power to take peace from the earth and to make men slay each other. To him was given a large sword."

The black horse is described in Revelation 6:5-6, "and there before me was a black horse! Its rider was holding a pair of scales in his hand." As a result of the wars from second horseman the black horse speaks of judgment and famine, for the rider carries a pair of scales (balances) used to weigh food and indicating its scarcity.

The pale horse is described in Revelation 6:8, "I looked and there before me was a pale horse! Its rider was Death, and Hades was following close behind him." "Those who escape death by the sword may die of hunger. Those who survive the hunger are likely to perish from disease (death)."