Blocks in the inventory are shaded differently from before / not lit enough

The bug

The blocks in the inventory are shaded wrongly / are not lit enough, in comparison with 1.14.4.
This can sometimes lead to confusion of blocks, especially in terms of colors (accessibility).

Examples

Here are (only) a few obvious examples:

• The grass block:
  1.14.4: 1.15:

• The leaves:
  1.14.4: 1.15:

• The banners:
  1.14.4: 1.15:

• The stone block:
  1.14.4: 1.15: