Brian Hoskin,I'm far from an expert on African religions or anything else. However, my interest in traditional West African folklore has led me to gather information about the Yoruba orisas {pronounced "orishas" whose tales read like stories of the Greek & Roman gods and goddesses.

See this excerpt from a Mudcat post I made in the
Folklore: Are Bright Colors Evil? thread:

"One explanation for the number of traditional African American songs about religious people dressed in red {such as "whose that yonder dressed in red/must be the people that Moses led"} is the association of West African deities with colors.

See this online passage:

"Shango
by Micha F. Lindemans
The god of thunder and the ancestor of the Yoruba people of Nigeria. He is the son of Yemaja the mother goddess and protector of birth. Shango (Xango) has three wives: Oya, who stole Shango's secrets of magic; Oschun, the river goddess who is Shango's favorite because of her culinary abilities; and Oba, who tried to win his love by offering her ear for him to eat. He sent her away in anger and she became the river Oba, which is very turbulent where it meets the river Oschun.
Shango is portrayed with a double axe on his head (the symbol of thunder), with six eyes and sometimes with three heads. His symbolic animal is the ram, and his favorite colors are red and white, which are regarded as being holy. In Brazil, Shango is worshipped as a thunder and weather god by the Umbandists. In Santeria, Shango (Chango) is the equivalent of the Catholic saint St. Barbara.

Shango was once the fourth king of Yoruba, immortalized after death."

Source: http://www.pantheon.org/articles/s/shango.html"

-snip-

In that thread I also mentioned the orisa Osun {Oshun} who is the Yoruba {Nigeria, West Africa}goddess of vain, flirtatious love, among other things. Although her color is the yellow of honey, there are images which depict her wearing a red piece of material around her waist.

Of course, none of this may have anything to do the question of why the reference to the color red shows up in early African Americans folk songs...

The color red is decidedly NOT a color that is wore to funerals by contemporary {or even 20th century}Christian African Americans. Females might wear red dresses or red suits to church during Christmas or a Valentine day social event, but in those contexts, the color red has no religions significance.