I've beheld the Tree of Life for many years now, and now I've started to paint my own as part of my neophyte tasks. I enthusiastically echo the importance of this. I've always known of some of the attributions, and I've also known there has to be a greater rhyme, or reason, but never really gave it much thought.
While I was painting the second, or
Ethical Triad, I thought: "Hey, these are the primary colors...", and suddenly a chain of revelations into the nature of the sephirothic color scheme blazed across my mind. The
Supernal Triad is archetypical, so of course, we have the foundation on which color, or sight are built . White, black & grey, or light, dark and shade. These are the rudiments of color in the way that
Chokmah's Forceful, and
Binah's Formative natures are the rudiments of masculine and feminine.
It is in the Ethical Triad we see the birth of the idea, the individual, the concept of perspective, this is where color is born. Here we have the primary colors
Chesed-blue,
Geburah-red, and
Tiphareth-Yellow. This evolution from white/black/shade to color is accompanied by an evolution from archetypical dichotomy, to the depiction of a King at peace, a King at war, and a beautiful man who is balancing these influences of Mercy and Severity to be strong yet just.
The third, or
Astral Triad brings us the secondary colors. We see chesed's blue has been enriched with the yellow of Tiphareth, and now emerging the emerald green of
Netzach. The same is true of
Hod's orange after Tiphareth's mediation of Geburah. Looked at sideways these are two triangles whose apex is Tiphareth.
Yesod is violet, and is the apex of a downward facing triangle whose base is Chesed and Geburah. The Astral Triad brings us the prism, the complete expression of color. Where is indigo, you may ask? Indigo is the color of the invisible Sephira
Daath. It does not follow the triangular arrangement of the others, nor is it below Tiphareth like the other secondary colors, but Daath is exceptional in every way. To come to think of it indigo is also unique in the prism, it is the only color of the prism not formed by merging two primary colors, but a primary and a secondary. The Astral Triad is of the mind, our dichotomy, and its reconciliation are now at their most sophisticated development before descending into the quaterny of Malkuth. The intuition, and the cognitive mind are balanced by the foundation of the Tree, Yesod: the blueprint ready to manifest, the realm of astral images, the collective unconscious, and so on.
Lastly
Malkuth is four colors: citrine, russet, olive and black. Four colors because Malkuth is the manifestation of the
Tetragrammaton: Yod He Vau He, Fire; Water, Air, Earth; South, West, North, East, etc. The colors of Malkuth are not bright like the others. They are not formed by simple combinations of two primary colors, instead they are muddled and dense. They reflect the nature of Malkuth, the physical universe. I've gone off on a tangent here, and must reel myself back in, but all of this blossomed my mind in the blink of an eye, while dipping my brush in the Yellow of Tiphareth.