cd “C:\Program Files\Oracle\Virtualbox”

VBoxManage setextradata “Yosemite” VBoxInternal2/EfiGopMode 4

Where N can be one of 0,1,2,3,4,5 referring to the 640×480, 800×600, 1024×768, 1280×1024, 1440×900, 1900×1200

      0       1 2   3       4 5

Tutorial by wikigain