I was confused at first, but it turns out these are actually the traditional representations. From Wikipedia:
In John's revelation the first horseman rides a white horse, carries a bow, and is given a crown as a figure of conquest,[2][3] perhaps invoking pestilence, or the Antichrist. The second carries a sword and rides a red horse as the creator of (civil) war, conflict, and strife.[4] The third, a food merchant, rides a black horse symbolizing famine and carries the scales.[5] The fourth and final horse is pale, upon it rides Death, accompanied by Hades.[6] "They were given authority over a quarter of the Earth, to kill with sword, famine and plague, and by means of the beasts of the Earth."[7]
I'd only ever heard Pestilence before, not Conquest. Conquest and War seem awfully similar to me as concepts.