Evolution of human colour vision lights, which appear to be clear. Other colour perception issues include having trouble distinguishing yellows from reds and violet, lavender and purple from blue. In other cases, objects that reflect both red and blue light may appear to just be blue to these individuals. Deuteranopes, who are missing medium wavelength sensitive cones, are similar to protanopes in that they cannot distinguish between colours in the green-yellow-red part of the electromagnetic spectrum. However, deuteranopes do not suffer from dimming issues. For example, purple colors are not seen as being opposite to other colours in the spectrum but instead appear to be
Road signs in the United Kingdom patch may only be coloured blue or green. Signs indicating a temporary change, such as roadworks or route diversions, are denoted with a yellow background. Usually these signs use a simple black on yellow colour code, more complex signage use the conventional signs superimposed onto a yellow background. In some areas, such as the Dartmoor National Park, additional signs and colours are used to distinguish road conditions. In addition to the national colour schemes, the park also uses white signs with a light blue border and text to denote routes suitable for medium-sized vehicles and white signs with a brown