I'm aware of that; it's just the documentation is a bit confusing.
I think what it's trying to say is that if you use ALLEGRO_PIXEL_FORMAT_ABGR_8888, then the following is not guaranteed to work:
// dest_ptr = 8 bit
*dest_ptr++ = r;
*dest_ptr++ = g;
*dest_ptr++ = b;
*dest_ptr++ = a;
But that this should work:
// dest_ptr = 32 bit
*dest_ptr++ = (a << 24) | (b << 16) | (g << 8) | r;
For this code, though, I think using ALLEGRO_PIXEL_FORMAT_ABGR_8888_LE would cause it to work on both PPC and Intel OS X.
However, none of this directly explains the other oddities with the image loading on PPC.
I just committed the updates to fix the endian issues to Allegro's TGA loader (seemed to only affect 32-bit images) and the native image loader. However, the native loader still produces garbage (although the colors are right now).
A screenshot of a JPEG file is attached.
TGA files are as posted earlier. (Almost correct, but with some horizontal artifacts.)
This could be an OS X 10.4 issue... whatever the problem is, the source data after loading the image is not the expected raw RGB values.