The origins of Halloween go back to pre-Christian times, to when Celtic groups in areas now known as Ireland, Scotland and Wales celebrated their New Year’s Day on November 1. This day was called “All Saints’ Day”, and October 31 was called “All Hallows’ Eve”. A great fire festival called “Samhein”on All Hallows Eve signaled the close of the harvest and the initiation of the cold and dark season of winter. All hearth fires in homes were extinguished, then re-lit from communal bonfires.
On All Hallows’ Eve, it was believed that the doors opened between the world of the dead and the world of the living. All the spirits of the people who died during the previous year were thought to be traveling from their resting place to their place in the next world. The Celts placed food and drink out to sustain the spirits, and people concealed their identity with disguises to supposedly escape harm while they walked from house to house to enjoy food and drink. Many people also carved turnips to represent faces, marking the origination of today’s jack-o-lanterns.
When Christianity took root in northern Europe, these folk customs were incorporated into a Christian framework. Samhein became All Saints Day, a day to commemorate all dead saints and martyrs. All Saints Day was sometimes known as All Hallows’ Day, and the night before, All Hallow’s Eve, or Hallow e’en, which we today call Halloween.
The Celts brought their folk customs to America with them, where they took root and evolved over the years. Halloween was originally celebrated in America as a harvest festival. Carved turnips became carved pumpkins, which grew in abundance in America. Colorful costumes replaced disguises, and trick-or-treat evolved from presenting food and drink to the wandering spirits.
Courtesy The National Confectioners Association
I then took some black spray paint and gave a quick blast into the eye sockets, nose, jaws, and any other deep pockets. A final coat of eggshell/off-white is applied with a dry brush technique so as to only cover the top surface. You don't want the light color going into the cracks and deep recesses...like the spaces between the teeth. 
Finally we give the skull a quick spray with green primer and black spray paint from about 2 feet away so as to lightly dust it with color.
