Colorful mandala is a signature symbol of Tibetan Buddhism's deep meditative practice. Different lineage has its own signature mandalas for students to meditate. Each master will select a special mandala (out of many of his lineage) for each student to meditate, according to the special individual mind-body attributes of each student. A path is laid down. A bridge is built.
According to chapter six of the Diamond Sutra:
"That's why Thatagata often told you: Monks, you must always remember my Dharma-as-a-raft metaphor: Even my Dharma can be cast away, more so for those unrelated to my Dharma."知我說法,如筏喻者,法尚應捨,何況非法
The bridge is to be cast away. What is the meaning of casting the bridge away in mandala meditation?
Carl Jung has the following interesting comment on the subject. Essential it means the master's mandala should be treated as a conceptual blue-print, rather than a concrete blue-print. In order words, the master gives a specific mandala concept (with attributes defined by a specific mandala), and from this guideline (the raft), a student builds his own unique mandala, the process of individuation according to Jung. This is Jung's passage:
In 1938, I had the opportunity, in the monastery of Bhutia Busty, near Darjeeling, of talking with a Lamaic rimposhe, Lingdam Gomchen by name, about the khilkor or mandala.
He explained it as a dmigs-pa (pronounced “migpa”), a mental image which can be built up only by a fully instructed lama through the power of imagination. He said that no mandala is like any other, they are all individually different. Also, he said , the mandalas to be found in monasteries and temps were of no particular significance because they were external representations only.
The true mandala is always an inner image, which is gradually built up through (active) imagination, at such times when psychic equilibrium is disturbed or when a thought cannot be found and must be sought for, because it is not contained in holy doctrine. The aptness of this explanation will become apparent in the course of my exposition.
The alleged free and individual formation of the mandala, however, sould be taken with a considerable grain of salt, since in all Lamaic mandalas there predominates not only a certain unmistakable style but also a traditional structure. For instance they are all based on a quaternary system, a quadratura circuli, and their contents are invariably derived from Lamaic dogma. There are texts, such as the Shri-Chakra-Sambhara Tentra, which contain direcctions for the construction of these “mental images.”
In Taoist deep meditation tradition, the meditative process of individuation (or enlightenment) is simply conceptualized as breeding an embryo. A new being is built. It has no visualization, though Jung has mentioned the metaphor of Gold flower from the title of a classic Taoist text The secret of the Golden Flower 太乙金華宗旨. In the establishment of Zen Buddhist, a flower and a smile is also put up as definitive symbol. Round, flower, new being seem to be the key attributes of these practices, as seen from classic texts. Oral (and importantly experiential) tradition fills the unspoken words, as always in the inner practices.
With the same human psychology, the conceptual path is always the same.