Doesn't make (much) sense...
I would just fill up the extra digits with 0, 0xc0c0c0c becomes: 0xc0000000 0xc00000000 xc00000000 xc0000000
But in the end everthing after the 1st 2 digits will be ignored anyways, as there is no HW (in Amiga context) that actually uses more than 8Bit per color.
32Bit per color only makes sense if you are doing lots of image-manipulation to miminize rounding errors (think PhotoShop).
edit:Too slow
