Yellow: the colour that arrives first

Yellow reaches the eye before the rest of the frame does. A mustard field, one leaf that has started to turn, a single lit window in a grey street: you have already looked there before deciding what you are looking at. It sits so high on the brightness scale that it behaves less like a colour and more like a small source of light.

It is also the first colour to break. Yellow clips before red, and a meter reading a bright field will pull the exposure down until everything around it goes muddy. People who shoot rapeseed in spring learn to close the aperture half a stop and leave the rest to the shutter, or simply to wait until the sun is low enough that the yellow comes back warm instead of raw.

On a screen the same thing happens, more quietly. A large yellow area lifts the whole desktop and leaves icons with nowhere to sit; a small one, a lamp or a leaf or a stripe near the edge, does the same work without taking the room. Yellow is best kept as a detail you find, not as the surface you look at all day.