I found a pretty good article on this in Fine Scale Modeler's "Modeling The Second World War" published in January or so of 1996. The B-24 squardons were having such a difficult time getting organized they came up with Assembly Ships. These aircraft would take off with group and give them a visual point of reference to assemble prior to heading to the target. Once the group was assembled they would return to base rather than continue the mission. The article used as reference Roger Freeman's book "The Mighty Eighth".
They were painted with high visibility colors such as yellow, red, white, and probably whatever was handy. Geometrical shapes such as circle and triangles were used with the occasional face painted on for good measure.
If you like I can scan the article and email it to you.
Dave