Orange and Black colors are used because orange represents the colorful fall harvest. Black represents the darkness of winter.
The Irish placed candles in turnips to keep away spirits. over time pumpkins got used instead.
More than 2000 years ago, the Celts celebrated the New Year on November 1, which marked the end of summer and the harvest( representing life), and the beginning of the dark, cold winter (representing death). they believed ghosts and spirits roamed the earth on October 31 to cause trouble and ruin crops. So the Celts built sacrificial bonfires and donned masks and costumes made of animal skins and heads to avoid being recognized as human.
It’s thought that the tradition of bobbing for apples originated from the Roman harvest festival that honors Pamona, the goddess of fruit tress.