Ubuntu virtual display help?

When the computer says that the virtual machine windows is optimised to work in 32 bit color mode but the virtual display is currently set to 16 bit. What does it mean and what should i do? Im using a 64 bit computer , but installed virtual box via. VirtualBox 4.2.12 for Windows hosts x86/amd64. I only had a virtual machine, which is using latest features, Ubuntu 13.04 , 64 bit.