The earth beads of an abacus are located on the left side of the abacus and there are five so that you can move the whole row to equal one heavan bead.
The earth beads are supposed to be different colored than the heavan beads and are usually colored black to show that they are earth beads.
Normally the earth bead is colored the same as the heaven beads because of stuff available. If the stuff can be used then the correct colors will be showen by black marble or black painted wood or dark wood.