The range of colours is enhanced by hot weather through the summer and early autumn. The colours, created by pigments of anthocyanins and carotenoids are produced in great quantities in hot sunny weather but are disguised by the green chlorophyll until the autumn, when the chlorophyll starts to breakdown exposing the underlying pigments.
The more anthocyanins produced the redder the colour, anthocyanins and carotenoids give orange colours whilst carotenoids on their own make yellow colours.
Some of the best examples of autumn colour are found on the Liquidambar styraciflua (American Sycamore) tree whose leaves change from a pale green summer shade, to a glorious mix of lemon-yellows, crimsons and saturated purples.
Japanese maples also take some beating for reliable colour displays, with the likes of Acer palmatum that has leaves that turn a fabulous red-orange colour, striking on a sunny autumn day.