The orange is the colour of the Buddhism, actually also are the yellow and the red, and the orange is on the half way of both. The orange is the colour of energy, happiness and triumph, but also the danger is generally shown in this color. Sunsets are normally orange, The orange color in the buddhism represents the ilumination, Actually is a hint of colour in the introspective life of these monks. 

Picture taken in Vientiane streets (Laos)