Revelation chapter 6:7-8
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. 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.
It doesn't say here 1/4 of the entire world's population died, just that "them" was given power over a 1/4 of the earth, particular countries on the earth, to kill with sword, hunger, death, and beast.
The colour of the fourth horse is given as deathly pale or sickly, yellowish green. Again comparing the Revelation with the Master's Olivet prophecy we find that the sickly pale horse symbolises pestilence: deadly disease epidemics and plagues that so quickly lay low millions of humans engulfed in war and famine. When the pale horse breaks into a gallop it will appear as though the finely tuned forces of nature have become dislodged. Disease epidemics of all kinds will sweep across the globe bringing death to millions of people and their crops. The rider on the pale horse has begun to ride below and death is following closely at his heels.