To reproduce:

1. Download and open attached project
2. Open "AdditiveSprite" scene
3. Select "bird-sprite_additive" gameObject in the hierarchy
4. Change Sprite Renderer's Color property to black

Expected result: Sprite changes it's color according to Color set in the Sprite Renderer's component.
Actual result: Sprite appearance does not change even if color in Sprite Renderer's component is changed.

Reproduced with: 5.6.0b1, 5.6.0b3.
Not reproduced with: 5.5.0p3, 5.4.3p2, 5.3.7p2.

Note: Only occurs when Material of the sprite is set to Additive.