I looked at several profiles of Spad XIIIs from Alan Toelle, and it appears the stabilizer bar is painted in the color of the underside. While the fabric colors contained aluminum flakes which gave the finish a "wet" look, the paint used on the metal and plywood areas contained no aluminum flake and were similar to an enamel paint, called ripolin. If the underside color was ecru, then the struts were probably a ripolin color similar to the ecru color. If the underside color was blanc=bleute, then the struts would be painted a ripolin similar to the blanc-bleute color. The aileron arms could be painted similarly, but I have seen some period photos that show they are dark, so black could make sense. I have seen one restoration that has the arms as French blue, which was used on some metal fittings.