Revelation 9:17-19

17And this is how I saw the horses and their riders in my vision: the riders had breastplates [the color] of fire and of hyacinth (sapphire blue) and of brimstone (yellow); and the heads of the horses looked like the heads of lions; and from out of their mouths came fire and smoke and brimstone (burning sulfur).

18A third of mankind was killed by these three plagues—by the fire and the smoke and the brimstone that came from the mouths of the horses.

19For the power of the horses [to do harm] is in their mouths and in their tails; for their tails are like serpents and have heads, and it is with them that they do harm.