Currently, the framebuffer device implemented only supports the mode selected in MacOS before booting into Linux, also supports 1, 2, 4 and 8 bit colours modes.
Framebuffer suboptions are selected using the following syntax
video=macfb:<font>:<inverse>
You can select fonts such as VGA8x8, VGA8x16 and 6x11 etc. The inverse option allows you to use reverse video.