''When WK550 arrived in this country the red was rather more orange yet darker than the red on either WK507 or WG478''
Both WG478 and WK550 were EFTS aircraft. I know that 478 didn't have a major serviceing in the last three years of service, I'm not sure about 550, but I suppose from what you said, she did. The first batch of majors done outside the RAF were done by Slingsby's at Kirbymoorside and the paint jobs weren't the best. The marking positions weren't standard and the edges hadn't been rubbed down. When the groundcrew tried to wet and dry them down, it was a tough job as the paint was very hard. it was suggested that it was a two pack polyurethane rather than the more usual cellulose. Later majors were done by CSE at Oxford. They looked better, but the paint was the one I mentioned that had an orange hue. I suspect 550 had the job done there. Also, the paint on the fabric areas cracked as it wasn't as flexible.