I have been looking at getting some panels re-painted so inevitably I've been looking for paint codes. I have unearthed a very useful thread on the Aprilia AF1 125cc page from 2021, for more colours view it here
For the 89 Sintesi Replica it looks like the following are correct:
Red = Rosso Custom JBT2
Lilac = Viola Chiaro JBR8
Turquoise = Turchese JLR4
