Very often in American folk music a Yella Gal, Yaller Girl, Yalloo or Yellow girl referes to a woman of mixed parentage. Specifically a Mulatto. "The Yellow Rose of Texas" mentions a woman who according to some historians was a Mulatto woman who kept Santa Anna busy in the sack while Sam Houston surrounded him at San Jacinto.
Further mentions of Yella Girls are found in Sea Chantys
"Why do them Yella girls Love Me so? Heave away Santy Anno, Because I won't tell them all I know, Along the plains of Mexico,"
I like the corruption of Dou Dou into Doodle, I certainly makes sense from the anglification (neat word Huh?) stand point.
Don