Black onyx is black.
Onyx helps separate and guards you from your negative emotions and help you cope and heal from sorrow and grief. If you are in an unhappy or any relationship where you cannot overcome the negatives in it, it can help you release from that person. Onyx can help defend against negative attacks and people. Black stones are the absence of light and are thus said to help make you invisible to the negative. It helps with self confidence and ego as well as building your responsibility and sharpens your senses, especially against negative Nancies.
Onyx is associated with Saturn, the Capricorn Zodiac sign and is a July birthstone.