Here's the color code:
Yellow - 12ga romex for power
White - 12ga speaker wire (some is 12-2, some is 12-4)
Gray - 22ga balanced cable (XLR)
Orange - CAT6 for Ethernet (wired home network)
Green - CAT6 for CobraNet, USB over CAT6, HDbaseT, s-video
Black - RG-6 for stereo audio, component video...