With the recent overhaul to Minecrafts rendering system, 2d rendered objects such as Tall grass, plants, fire, etc now have a dark shading on them similar to normal blocks on its difference faces.

Fire now has certain sides that are darker than other sides, tall grass now has some pretty dark shading which makes tallgrass much darker than previous versions and makes them stick out.

Sun flowers, double plants, etc also have dark shading which dulls the color of everything out.

This issue also gets worse if you view them from far away, presumably from anisotropic filtering and mipmapping. The objects will have dark black outlines all over them making them very ugly.