When mining blocks with a block above them, the mining particles are black like shadows. When the block above is air the particles are the colour of the block being mined as I expected.
MC-47757
Mining Particles are Black
Resolved
Duplicate
0
John A Dunne
(Unassigned)
Unconfirmed
Minecraft 14w06b
Retrieved
Additionally note that you need to mine the bottom face of the block and the particles only stay black for a short amount of time.
(There seems to be no difference if there is a block above, or just air.) Also only affects opaque blocks.