I鈥檝e noticed that when an object is seen from a distance in daylight, the colours appear changed. For example, when I observed my wife walk round a lake in Switzerland, her pink top looked white and her blue trousers looked pink from 600 metres or more away. Do surfaces need to be sufficiently large in our field of view for us to perceive their colours correctly?
鈥� In the centre of your visual field there is a small area that is effectively blue-blind. 鈥� means that objects with colours that differ only in how much blue they contain become indistinguishable when they are very small 鈥� about the size of a tennis ball viewed from the other end of the court. So white and yellow will look identical, as will red and magenta, or blue and black.
This phenomenon has been known empirically for a long time. Naval signalling flags are designed so they cannot be confused even when viewed at a distance where this effect could manifest itself. Similarly, heraldic rules forbid a yellow emblem on a white background or vice versa, or blue on black, and so forth.
Advertisement
Roger Carpenter, Professor of Oculomotor Physiology, University of Cambridge, UK
鈥� This effect is called aerial perspective and is an important technique in a landscape painter鈥檚 toolbox. Diluting colour intensity by blending it with white mimics the effect of the atmosphere on distant objects.
This effect is the reason faraway hills have a bluish or purple tinge, and why the colours on your wife鈥檚 clothes appeared pale. In a landscape painting, bright colours such as reds and yellows are best used in the foreground, whereas pale blues and other diluted colours will give the illusion of depth. Of course, the broke all these rules, favouring strong colours over realism with wonderful results.
Ingrid Banwell, Sydney, Australia
We pay 拢25 for every answer published in 快猫短视频. To answer this question 鈥� or ask a new one 鈥� visit newscientist.com/lastword. Terms and conditions apply.
This article appeared in print under the headline 鈥淐oloured dots鈥�