Related:Do you have a Quadra 800, or a Centris / Quadra 650?
Daft question, but if you do, could you install it in one and check if it does millions of colours? The onboard video is hobbled so it doesn't and I'd be interested if that carries over to the card.
The DAFB (framebuffer controller) on my Quadra 700 has a different part number so I dismissed it, but I found this image which clearly has a 343S0128-01 populated in the DAFB, which lends credence to the notion that this is a duplication of the Q700 video subsystem...
I can't identify the 343S1075, however on my Q800 the DJMEMC and IOSB are -1077 and -1078 respectively so it is of that era...
Edit:
The 343S1075 is used on the 8-24GC