Note how the first four trigrams begin with a yin line and the second four begin with yang. Within this there are four pairs whose first and second lines are the same. Thus this sequence shows the trigrams in order from most yin to most yang. This colour scheme tries to make a more yin trigram darker than one that is more yang.

Within that rule the colours are meant to harmonize with what the trigrams represent. So gen is the colour of heather on a distant mountain and kan is the colour of deep, swirling water. Xun (penetrating wind or wood) is the growing colour of spring green, when the sap rises. Brown is the growliest colour, most appropriate for zhen, thunder and li (clinging fire or brightness) has to be the brightest colour, yellow. Dui is an exception: pink is the colour of joy and openness.

Stephen Karcher makes much of the "cycle of time". In his I Ching: The Classic Chinese Oracle of Change Karcher points out that gen (mountain) represents the still point at the end of one cycle, after which zhen (thunder) awakens the earth to a new spring. Opposite gen is kun (field), another still point where the opposing forces on either side are neutralized.

From this he deduces two hemicycles. The yang hemicycle represents growth, activity. It starts with the thundrous zhen, develops using the subtly penetrating power of xun (wind or wood) and culminates in li (clinging fire or brightness). After kun comes the yin hemicycle, which he identifies with formation. The open joy of dui first expresses the form which is them manifest by qian and levelled or "trued" by kan (chasm or deep water).

This scheme attempts to express Karcher's insight using colours that bring out the hemicycles. Kun and gen are culminating points; yellow is the colour of earth. Between them are bright colours for spring and summer, or darker colours for autumn and winter.

This arrangement comes from LiSe Heyboer's Book of Sun and Moon website. The guiding principle is the way the yang lines add to white (qian) like light, while the yin lines accumulate to black (kun) like pigments in paints or dies. Connie Achilles' analysis of masculine colours (red, green, blue) and feminine colours (cyan, magenta, yellow) is interesting but, I suspect, coincidental.

Danny Van den Berghe has an article on FourPillars.net called The True Colors of Trigrams. He makes an interesting case for using warm colours for summer and cool colours for winter and demonstrates that the same colours also work with the five elements and the Early Heaven trigram sequence.

These are the colours Stephen Karcher uses on his Universal Compass, described in his I Ching: The Classic Chinese Oracle of Change. More about time cycles can be found at GreatVessel.com.