So what's the mechanism for producing a chimera - apart from scientists swapping foetal cells around?
It occurs naturally too. It's the fusing of two (or more) fertilized eggs. It occurs in humans, too, which is where we get people with different colored eyes, and how people can actually have children that aren't theirs, so while they did produce them physically, the DNA in the children came from a parent's fraternal twin that fused with them in-vitro, so they will test negative for a maternity or paternity test. It's also one way we get intersexed and hermaphroditic humans and other animals.
I'd look suspiciously at those with three-color-hair types, too, though I'm not sure about that one being for-sure chimeraic... Ever seen a man with a different color moustache and different color beard and different color hair to boot? I've seen a few.
Here's a wikipedia article definition of it... (I know, wikipedia? lol) but it's close enough:
http://en.wikipedia.org/wiki/Chimera_(genetics)A chimera or chimaera is a single organism (usually an animal) that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. If the different cells have emerged from the same zygote, the organism is called a mosaic. Chimeras are formed from at least four parent cells (two fertilized eggs or early embryos fused together). Each population of cells keeps its own character and the resulting organism is a mixture of tissues.