I was wondering: in the Self-Realization courses, Yogananda talks about different symbols seen at different chakras, such as a blue ball, red triangle, white half moon, yellow four-angle figure. Are these figure seen "real"? And what is the purpose of these figures? What does for instance, a blood red triangle have to do with the lumbar chakra?
Yogananda indeed writes about the colors and shapes you mention above. They are, according to him, the true colors and shapes we see when our life-force is fully withdrawn from the body into our deep spine, into the chakras, and when it rises upward.
The colors we usually hear about, the rainbow colors (red in the muladhara, orange in the swadhistana, etc.) are actually not part of Yogananda’s teaching, nor of any ancient yogic lore. They are simply a practical way of practicing with the chakras (Swami Kriyananda did too), but they are not the deep inner experience of them.
Swami Kriyananda explains it in his enlightening book, The Essence of the Bhagavad Gita:
Indeed, the clear vision of that light reveals a differently colored light in each chakra, which is seen in the spiritual eye: yellow for muladhara; white for swadisthana; red for manipura; blue for anahata; smoke colored, with little specks of light, for bishuddha; and in the spiritual eye, as has already been described, a ring of gold surrounding a field of deep blue-violet, with a silvery-white five-pointed star at the center.
It is tempting to compare the colors of these six chakras, along with the seventh in the so-called crown chakra at the top of the head, with the colors of the rainbow. The rainbow is certainly comparable with the seven chakras, especially with their gradual change in hue from materialistic red to spiritual violet (red, orange, yellow, green, blue, indigo, and violet). This comparison must be written off, however, as more poetical than literal. The colors stated above by Paramhansa Yogananda are the actual chakra colors seen in the spiritual eye.
The ancient text Gheranda Samhita, in its five concentrations (dharana) on the elements, explains quite similar colors and shapes to the ones Yogananda teaches.
So what do these colors and shapes have to do with our various chakras?
The first five chakras manifest the five elements of which all creation is made: earth, water, fire, air, ether. So the colors and shapes represent these basic elements.
1. MULADHARA: the color of the EARTH chakra is yellow, not a bright yellow, but an “earthy” yellow. The square too is an “earthy” symbol. Swami Kriyananda writes: “The things related to human life and to earthly existence in general might be described as four-square.”
2. SVADHISTANA: in the WATER chakra we inwardly see a white half-moon, Yogananda writes. Water is the feminine element, like the moon, and white expresses its purity.
3. MANIPURA: in the FIRE chakra see a blood-red triangle. Fire is red, like the planet Mars. The red triangle seems a divine symbol of fiery ascension.
4. ANAHATA: in the AIR chakra we see a round ball of palpitating blue. Air is (or appears) blue.What does the palpitating ball-shape have to do with “air”? You may meditate on it.
5. BISHUDDHA: in the ETHER chakra we see a smoke color, checkered with luminous specks of lights. “Smoke-color with lights” in fact seems to resemble the cosmic ether.
6. AGYA: Then there is the Christ chakra, above and beyond the five elements: you see a ring of gold surrounding a field of deep blue-violet, with a silvery-white five-pointed star at the center. These three colors represent the Eternal Trinity of God: the gold is AUM, God’s primordial vibration (Holy Ghost); the violet-blue is TAT, or Christ Consciousness (the Son); the white star is SAT, or Cosmic Consciousness (the Father).
7. SAHASRARA: this highest chakra is beyond any vibration, color, shape, time, and dimension.
This was a deep question. The main thing is, such things shouldn’t stimulate our intellect but our desire to meditate and to see them ourselves.
So God bless your inner vision, produced by increasing stillness,