Is orientation-specific color adaptation in human vision due to edge detectors, afterimages, or "dipoles"?

After one looks alternately at red vertical and green horizontal stripes, vertical and horizontal white stripes appear greenish and pink, respectively. This color aftereffect might imply that contour-detecting cells participate in human vision, or might simply be due to afterimages. A procedure that precludes afterimages still yields aftereffects, but sensory units less complex than edge detectors could be responsible.