6 meters' pallisade 'hid Stonehenge'

From Stonepages: A 20ft-high palisade hid Stonehenge 5,000 years ago.

Apaprently such a high visual barrier, surrounding most of the complex, prevented the common of mortals from snooping into the rituals that were performed at the British monument.

My question would be: what color was it painted of? (Ok, silly question).