This thread prompted me to have another try, and I managed to find a suitable resolution even though native was only listed. I also noted that the MacBook ignored the timeout, so added line #3.
This is my current grub.conf:
GRUB_DEFAULT=0
# GRUB_TIMEOUT_STYLE=hidden
GRUB_RECORDFAIL_TIMEOUT=3
GRUB_TIMEOUT=3
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
GRUB_GFXMODE=1152*864*32
GRUB_GFXPAYLOAD_LINUX=keep
# GRUB_TERMINAL=gfxterm