White Horse - Conquest/pestilence. The rider carries a bow with no arrows, and wears a crown symbolizing a nonviolent rise to power. Holds the power of the Conquering, and to conquer also depicted as a hollow suit of armor from which bugs emerge.
Red Horse - The rider of the second horse is generally held to be gaining and represents War. The red color of his horse represents blood spilled on the battlefield. He carries a greatsword, which represents battle and fighting.
"Revelation 6:4 - "And there went out another horse that was red: and power was given to him that sat thereon to take peace from the earth, and that they should kill one another: and there was given unto him a great sword."
Black Horse - The third horseman, riding the black horse, is called,Famine. The black color of the third horse could be a symbol of the dead.
"Revelation 6:5 - 6:6 - “And when he had opened the third seal, I heard the third beast say, Come and see. And I beheld, and lo a black horse; and he that sat on him had a pair of balances in his hand. And I heard a voice in the midst of the four beasts say, A measure of wheat for a penny, and three measures of barley for a penny; and see thou hurt not the oil and the wine."
Pale Horse - The fourth horseman is a sickly horse, which may be the source of the notion of "pestilence" as a separate horseman, but is explicitly named Death.
"Revelation 6:8 - "And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth."