EMERALD

Emeralds are traditionally a deep green color or some shade of green. The darker the color green, the more expensive the emerald becomes. It is a variety of beryl which is a clear transparent gem that comes in several colors. The emerald is somewhat fragile and it is difficult to find a “perfect” emerald. It is the birthstone for the month of May. It is ranked along with diamonds, rubies, and sapphires as the top stones for jewelry.

JASPER

The first mentioned stone in these verses is jasper. There are a variety of colors associated with jasper but the greenish color is the most desirable.
An early variety discovered in India and still mined there today is called bloodstone. It is dark to medium green with small spots of red scattered throughout. It has been said that it originated when Christ's blood fell to the ground and was scattered on the rocks under the Cross,

GREEN, VIOLET, AND BLACK

Searching out the meanings of these colors took a little more effort.

Green is the color that represents joy, hope, and the bright promises of youth. According to the source I studied this symbolism is used in the Catholic Church.

Violet is normally used around Easter and Lent; it shows the suffering and purifying effects that come as a result of chastening. Again, this symbolism comes from wihtin the Catholic Church.

Black seems to be a pretty obvious color since in most cases today we use black to refer to death. Black does indeed represent death but it can mean sorrow, and mourning. Darkness fell over the earth just before Christ died and his time in the tomb was for 3 days. Dark=black. As far as this color being mentioned in church, it is seldom used except for Easter.