**Ricardo Bernárdez-Vilaboa**

Professor in Optometría y Visión Department, Univeridad Complutense de Madrid, 28044 Madrid, Spain; ricardob@ucm.es; Tel.: +34-649-172-142

Received: 5 September 2020; Accepted: 23 September 2020; Published: 25 September 2020

**Abstract:** Colour is important in art, particularly in pictures. The eyes receive images with a particular condition after traversing the cornea, other surfaces and interior liquid of orbit. It is possible for changes in colour to be perceived when pictures are viewed by one eye that has defects in any surface. Cone defects are directly related to colour failure. Can the original colour be recovered by modifying the visual function? There are multiple colour tests, but there is no consensus on which colour test is best. After detecting a problem with colour, we found several techniques to enhance colour contrast for dichromats. Treatments considered were reversible and innocuous and combined with melanopsin-based blue light sensitivity for melatonin suppression, allowing visual acceptance and luminous perception. A light source of 4000 K with a Duv value of zero, a good observer and adequate illumination were necessary. Subjective assessment may be affected by visual functions such as accommodation, binocular vision and quality of the eye.

**Keywords:** colour; art; visual; accommodation; binocular vision
