Final answer:
Synaesthetic colours result from unique brain connections that allow for cross-sensory experiences, such as seeing a colour when hearing a sound. This notion parallels Kandinskii's idea of colour's psychic effect on the soul, which goes deeper than the physical properties and theories of colour vision.
Step-by-step explanation:
According to the model of synaesthesia, synaesthetic colours result from unique neural connections in the brain. These connections prompt synaesthetes to experience a sensory stimulation, like hearing a sound, and simultaneously perceive a colour, which is not present. This might be due to cross-activation of different sensory areas in their brains. Kandinskii suggested that colours have the power to produce a psychic effect, influencing the soul directly beyond superficial impressions and engaging it in a deeper and intensely moving manner. This is similar to the psychological aspect of synaesthesia wherein colour associations go beyond simple color perception as explained by the two main theories of color vision: the trichromatic theory, which deals with how three cone groups in the eye process color, and the opponent-process theory, which describes how colours are processed in opponent pairs.
In synaesthesia, colour experiences may also be interpreted as an extension of the psychic effect that Kandinskii speaks of, where colours create a vibrational impact on a sensitive soul. These experiences are a step beyond the physical interpretations of colour, appealing directly to the spiritual or emotional realm of the individual.