The Codex Symbol, called this because it is on the cover of the Codex of Ultimate Wisdom, is a simple but very clear way to show how the Eight Virtues are founded on the three principles of Truth, Love and Courage, by assigning each principle a color, and each Virtue is a mix of the colors of the principles on which the Virtue is based.
First there are the three circles of the three principles of Truth, Love and Courage, which are the foundations of all the virtues (with exception of Humility).
Then come the Virtues of Honesty, Compassion and Valor, forming a triangle around the three circles. Each of the three lines only touch one circle, since these virtues are only founded on one principle. Therefore, the three lines have the same colors as the three circles.
Then come three more lines, which roughly form a headstand triangle. These represent the virtues of Justice, Sacrifice and Honor. Since each line touches two circles, because these virtues base each on two principles, they mix the colors, resulting in green, orange and purple.
The small circle in the center is the virtue of Spirituality. It touches all three circles, since the virtue is based on all three principles. All three colors mix into white.
The outer circle represents the Virtue of Humility. Since it is independent of the principles, it touches no circle, it has no color, and is therefore black.