I wonder if the red was a temperature issue?
When the RAF bought the Slingsby as a trainer they had to get agreement with Slingsby to have them painted in yellow, the fibreglass wings being very temperature critical, indeed even the none slip walkways were usually white.
They then bolstered the fleet by adding G- HONG and KONG ( from Hong Kong naturally ) and put them through the spray shop to match the rest of the Hunting fleet In Yellow..... when Slingsby learnt of it, they were required to put them back through paint shop to revert to white, due to being and earlier version and being even more temp critical.
Luckily for the paint shop when looking at removing the yellow paint, one of the guys found that it hadn’t bonded correctly and literally peeled off as one sheet. The paint company agreed it was faulty so provided the new paint for free.