My friend dr.sbdink recently asked me why there can sometimes be a rainbow-like sheen on raw meat or fish, whether "colourful" meat is safe to eat. I told him told him not to worry as it has something to do with the proteins oxidising-- I was right on the prescription, but wrong on the reason. Consulting Dr. Wolke's handy book, I found the right explanation.
Those colourful waves you see on raw meat are actually an optical illusion caused by the slicing process. When you cut across the muscle fibres-- myofilaments-- with a sharp knife, the tips of those fibres can play with light. The transluscent tips of the myofilaments-- through birefringence or diffraction (or both)-- cause light waves to interfere with each other, breaking up light into its component parts (i.e., the colours of the rainbow). Basically, it's the same reason you see "rainbows" through some crystals or on CD's. Note that this can only happen if the knife is sharp-- for the colours to appear, you need the surface and the myofilament tips to be fairly flat, not torn or squished by a dull knife.
So next time you see meat with a colourful sheen on the deli shelf, worry not-- it just means they sharpen their blades. But it's a totally different story if the colour on the meat is not a sheen but a solid greenish mass.