Black is absolute colur.

Symbolizing are night, dark, secret, embodies for infinity and female vital force, for allowing a non ending ending, forming for inside stability, strengthens for force soul.

White is clean colour, and spirituality, virginity, individuality,  concentration, filling with energy, cleans and raises.

Grey colour is neutral color of white and black, helping for balance condition for opposites, as for feeling failure, and depression.

As in in your mandalas are harmonized colors combines for a seven colors of rainbow, as meaning for rainbow feeling, and rain  ,like for embodies as  arc element  connection between as symbol for magic soul rebirth.