Humans see colour differently in summer, with yellow seeming more green than in winter, scientists have shown. Researchers at York University, in the UK, looked at how colour perception changes between seasons and in particular how humans process a colour known as "unique yellow".Humans identify four hues - blue, green, yellow and red - that do not appear to contain mixtures of other colours.Unique yellow is particularly interesting to scientists because it is stable across large populations - everyone agrees what unique yellow looks like despite the fact that eyes differ considerably.The researchers wanted to discover why this colour is so stable and what factors might change how it is perceived."What we are finding is that between seasons our vision adapts to changes in environment," said lead author of the study report Lauren Welbourne."In summer, when there is a lot of foliage, our visual system has to allow for being exposed to far more green. It's a bit like changing the colour balance on your TV."This is the first time natural changes in the environment have been shown to affect our perception of colour." ..