Thanks Charly - I assumed it was all done by layering, I didn't realise that something more tricky was going on. If you need me to combine any layers, I could do that.
I've discovered that OO-CIR's wingtips are not typical. When looking for others to paint based on this design - there are many of them - more seem to have a partially coloured wingtip with a striped design on it.
https://www.airliners.net/photo/Untitled/Cessna-172N-Skyhawk-II/7563865/LI'm not sure how those are done in OCR. Obviously the work involved in covering every little variation is excessive, and I think the version in the above image would be better. I may try painting a full 172 with that option and then make a replacement wingtip template from it, assuming I can make it work.
My overall plan is to make two more 172 patterns and then two or three Cessna 150/152s, since there are limited options for that type.
It would be good if there could be a community of painters volunteering some time, but I don't see that happening, unfortunately.