Demon eyes drop 0-2 demon eyes when killed. When eaten, a demon eye restores 2 (🍗) hunger points and 3.2 saturation points, giving a nourishment value of 1.6. It also applies a Poison effect lasting 4 seconds to the player, causing 4 (♥♥) damage, which reduces hunger/saturation by 6 points.
If Demon Eyes are displaying as white dye, it means that the resourcepack is not enabled. The resource and the datapack are the same .zip so be sure to put the datapack in your resourcepacks folder aswell. If you're on forge it may be because your mod resources are below Minecraft in the resourcepacks list.