The Expositor's Bible Commentary says this about the color of the fourth horse: "'Pale' ( chloros ) denotes a yellowish green, the light green of a plant, or the paleness of a sick person in contrast to a healthy appearance." Put bluntly, this horse is the color of death .
Revelation 6:[7] And when he had opened the fourth seal, I heard the voice of the fourth beast say, Come and see.
[8] And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him.