in the case of 9vx running on Linux it's x8r8g8b8, drawterm on osx is
also x8r8g8b8.

here's how it breaks down drawing to display:

source        destination              error
XRGB32     XRGB32                 no
XBGR32     XRGB32                 no
ARGB32     XRGB32                 yes (see attached)
RGBA32     XRGB32                 yes

i've done a bit more testing and will hopefully have a full table for
32-bit images later tonight: