The Bug:

The stem of a big dripleaf is rendered too dark in the inventory.

Steps to Reproduce:

• Give yourself a big dripleaf.

/give @s minecraft:big_dripleaf

→  Notice how the stem is rendered too dark in the inventory.

Information:

If you were to compare the stem of a big dripleaf, to the stem of a small dripleaf, you will notice that the small dripleaf's stem, is rendered much brighter than the big dripleaf's stem.