who told you that? Is this doing this everywhere or in special spots? You know, when one colors mortar, you think its real dark when its wet, but as it dries out, you later say I wish we would have added much more colorant. I am scratching my head in desparation about SALT.
As the mortar was drying or curing, did you spray it with misty water during the following three days? I know with grout, you should do this, not that anyone does it though.