Well just considering the engine options available for a convertible, if the VIN on that car was definitely for a V8:
Any of the SS RPOs would have normally had the D90 stripe, so special paint could've been for non-standard paint color, stripe delete or non-standard stripe color.
On the other V8 engine options 307, 327 and 350 (LM1 or L65), a stripe package D90, D96 or DX1 was optional. That I believe at least rules out the stripe delete possibility, making it technically more likely that non-standard Camaro paint color would be the more probable on a special paint car.
I would be interested to know if you ordered (for example) an LM1 'vert and wanted an optional stripe but in a non-standard stripe color, would this trigger a special paint (-) trim tag? I'd think so, as Fisher would've needed to identify the non-standard detail, but then again the trim tag didn't address stripe color (or even which stripe option, for models that had optional stripes). Thoughts?