I would suggest looking at the aircraft produced by TVAL, Fred Murrin, and several others who are using original construction methods. They often have a semi gloss to a matt look and they are maintained to a high degree, and kept out of the sun. So I would say a more matt look for aircraft in service. I will defer to those more knowledgeable for WW1 era aircraft, but I do know that doped finishes on fabric areas for 30s and 40s era light aircraft such as Piper Cubs, Taylorcrafts, Aeroncas etc...were matt in appearance and did not match the glossy finishes on the metal parts such as cowlings and struts.