Azalea, birch and spruce leaves, unlike other leaves, remain the same color regardless of biome. However, the method used is inconsistent - birch and spruce leaves are gray with a constant tint, whereas azalea's texture is colored by default. According to the latest comment on MC-3930, this seems wrong, and would likely prevent the mentioned future recoloring behaviour.
Comments 4
Most likely intentional, as the idea of the azalea leaves are that they are always lush, similar to moss and the azalea bush. It would be weird if you were in a desert and saw this azalea tree that didn't look lush.
Can confirm.
This is not MC-213987. As stated, this issue is related to the method in which color is applied.