Burnout, recovery, and flow in youth high-performance athletes: a multilevel mixed-methods examination of mental health and psychological functioning in Chinese athletes.

Nearly one in seven individuals around the world were living with a mental health disorder in 2019, and this prevalence increased by 26%–28% during the COVID-19 pandemic (). The development of fast and inexpensive methods of diagnosis and ancillary treatment protocols for common mental health disorders is essential to address the global mental health crisis. For centuries, colour therapy has been used in traditional medicine, with practitioners exposing patients to coloured lights applied to different body areas to promote calm or energise, influence mood, and support physical and mental health (). Currently, colours are used as a complement in treating various disorders (; ; ; ), and colour therapy is advertised on websites. However, scientific evidence demonstrating the effectiveness of colour therapy is absent (). Since colours are associated with mood and emotions (), colours may potentially serve as markers of mental wellbeing, mental states, or mental health disorders (; ; ). Colour perception starts with light absorption by the three types of cone photoreceptors in the retina and can be described by three perceptual values (). Perceptually, colour is characterised by hue, chroma, and lightness, enabling the communication of colours by ascribing values to each of these three dimensions. One of the most common systems for this kind is the Munsell atlas, which is widely used in colour vision research (; ). Quantitative description of colour is based on the results of colour matching experiments, which form the basis of the Commission Internationale de l’Éclairage (CIE) XYZ and related colour systems (). While the CIE XYZ colour system and the Munsell atlas system provide accurate representations of colour for the majority of people, these systems do not describe colours as they are seen by 8% of men and 0.5% of women with colour vision deficiency (). Therefore, screening for colour deficiencies is essential in research. People usually communicate their experience with colours using colour terms, such as ‘red’, ‘green’, and ‘blue’. These terms correspond to concepts of colours, which have different symbolic meanings in different cultures (), and cannot be directly related to actual colours because they describe large colour categories with variable boundaries (). While the association between colour terms and emotions is largely defined by culturally specific symbolic meanings of the colour, the association between actual colours and emotions may tap into the unconscious mind that is less influenced by cultural conventions and therefore may be better suited as markers of mental wellbeing (; ; ).