So I've discovered that there are secrets in GT6, and I'm not sure if everyone knows so here:
14 of the Miatas have secret stripes that show up when repainted. Each has its own design and they are these variants:
Mazda MX-5 (NA) '89
Mazda MX-5 J-Limited (NA, J) '91
Mazda MX-5 J-Limited II (NA, J) '93
Mazda MX-5 Miata (NA) '89
Mazda MX-5 Miata J-Limited (NA, J) '91
Mazda MX-5 Miata J-Limited II (NA, J) '93
Mazda MX-5 Miata SR-Limited (NA, J) '97
Mazda MX-5 Miata S-Special Type I (NA, J) '95
Mazda MX-5 Miata VR-Limited (NA, J) '95
Mazda MX-5 Miata V-Special Type II (NA, J) '93
Mazda MX-5 SR-Limited (NA, J) '97
Mazda MX-5 S-Special Type I (NA, J) '95
Mazda MX-5 VR-Limited (NA, J) '95
Mazda MX-5 V-Special Type II (NA, J) '93
There's a particular model of Subaru that gets tinted windows when painted Chrome.
The BMW M3 GT2 Base Model becomes available to buy when the sponsored version is used in Arcade Single Race.