Efflorescence is when soluble salts migrate to the surface of the masonry and crystallise as they dry, forming white deposits.
This is a natural phenomenon and are usually caused by salts within the original clay that the brick is made from. However, they can also come from the ground or from adjacent masonry structures.
If the efflorescence is recent, then these areas should be left to weather naturally. Heavy deposits can be removed using a dry brush.
If the deposits are fairly insoluble and have been there for some time, then it is possible to tint them. However, this will not prevent new salts forming in the future.