Colour is the most obvious and probably most frequently described synaesthetic link. In the English-speaking world, the term chromesthesia (from Greek chroma: colour + aisthesis: feeling) is often used synonymously for sound-to-colour experiences. Typical of a “true” synaesthetic colour assignment is that it has no tolerance: even small deviations are perceived as “wrong”. On the other hand, the one and only match elicits a strong feeling of coherence. The synaesthetically associated colour can often be described precisely, but is difficult to reproduce by usual means, as a colour may contain other underlying colours, have a certain level of transparency or resemble a coloured light (photism).