VMQemuVGA.kext, it should work on all OSs from Snow Leopard up to Yosemite 10.10 under VirtualBox

Disable kext signing on OS X Yosemite

To use VMQemuVGA on OS X Yosemite, you need to disable the kext signing security setting. On a physical Mac you would use the following command:

nvram boot-args=kext-dev-mode=1

On a VirtualBox virtual machine the boot-args are stored in .vbox virtual machine settings file:

<ExtraData>
  ⋮
  <ExtraDataItem name="VBoxInternal2/EfiBootArgs" … kext-dev-mode=1 … "/>
  ⋮
</ExtraData>

You should be careful to only install system drivers from sources that you trust.