Coloured hearing is a form of synaesthesia with co-perception of acoustic stimuli as visual effects. In contrast to acquired or induced synaesthesia, the genuine form is thought to origin very early in life and to not relevantly change over time. Therefore, finding correlations between acoustic stimuli and visual effects with genuine coloured hearing and evaluating their visual significance even on adults gives hints on which acoustic properties have been significant for an individual since early life. With this snapshot of significance taken from many individuals, we hope to better identify the border between congenital perception and perception habits created from cultural influence. Knowledge about this border is essential for composition of contemporary music, as it marks the limit where musical parameters go beyond trainable perception and thus render irrelevant as compositorial means. So far, for a preparatory case study we developed a set of sounds, tested it on a single genuine coloured hearing individual and present first results.