For years our Scarf & Goggles Club included a restored Thomas-Morse Scout with "khaki" color scheme plus US cockades & rudder stripes. It was semi-invisible from above or anywhere near the horizon at about half to 3/4 mile. The white cowling was by far the easiest way to see it air to air.
Of course, those of us in Stearmans (and the N3N

) got lots of practice playing Spot The Tommy because it was so s-l-o-w.