...a black horse; and he that sat on him had...

This is the angel of death as a result of human policies. The angel carries a pair of balances in his hand to represent human justice (or injustice).  The voice crying out prices signifies unjust or unwise economic policies that result in inflation or famine. This angel emerges third because this is the next form of death to enter the world, as the stories of the society-wide wickedness behind the Great Flood and the destruction of Sodom and Gomorra indicate.  Also alluded to here is the great famine in Egypt which Joseph alleviated through wise public policy.