Here it is explained by the Denver spiritual community

The First Stage or The Lesser Work:

1. Saturn, Lead, black

This is the consciousness at its lowest stage of development. It relates to the thinking and passions of the material world, chaos. There is no understanding of spiritual things. The process needed to pass out of this stage is what the Alchemists called mortification, symbolized in the Bible by the death of the firstborn and the Passover of the Israelites.

2. Jupiter, Tin, gray

Once across the Red Sea this next stage is one of growth into the newly recognized spiritual person which must be undertaken to reach the goal. This is the development of the soul's receptivity. The Alchemists called it sublimation. It is represented in the Bible by the 40 year wandering of the Israelites, seeking greater understanding of what their God required of them.

3. Moon, Silver, white

The final stage of the Lesser Work is that of spiritualized, purified emotions and heart. The accomplishment of this stage, what the Alchemists called the completion of the Lesser Work, represents the regeneration of the feminine side of man. The lunar crescent has raised above, dissolved and now contains, all the potentialities of the soul which were in the original chaos of Saturn. They have now been united and purified. It is the perfection of the Heart, the Bride, and is represented by the Blessed Virgin. It is being reborn of water (heart).

The Second Stage or The Greater Work may be represented as follows:

1. (Image of Venus) Copper, yellow

The first stage of the Greater Work indicates the beginning of contact with the Holy Spirit. The very highest level of the human, + is just able to reach up to the lowest level of the Spirit, O. The Alchemists called this process crystallization. It is the birth of the Christ, the rising of the inward sun, which is only possible after the preparation of the Lesser Work.

2. Mars(Image of Mars) Iron, orange

The second stage of the Greater Work indicates an active descent of the Spirit into the lower levels of human consciousness. The body itself is completely penetrated by the spiritual forces from on high. This new creation is not yet perfect, for the spiritual sun, represented in the symbol, is not yet detached from the cross of the elements, the material man. This is called by the Alchemists coagulation. This transformation is one of the body into Spirit-become-form.

3. Sun(Image of Sun) Gold red

This is the final stage in the Greater Work. It represents the completion of the embodiment of the spirit. It is the highest level of the intellect, or masculine. The Alchemists called it the completion of the Greater Work. The Sun or Spirit has now incorporated all aspects of the lower, material intellect. This is the red; the fire. The completion of this process is the Baptism by Fire. This is the Bridegroom. It is symbolized in the Bible by the resurrection.