The rainbow trout gene pool is fairly massive and includes an awful lot of variation. I guess strictly speaking, all the Rocky Mountain/Pacific trout, from Gila, to wild California golden, to steelhead to red band and likely even to cutthroats, are part of an extended rainbow trout family. Kind of like brown trout including a range of creatures from softmouth trout in Serbia to Altas Mountain trout in Northern Africa to the various German, Scottish and Irish strains of stay-put trout and sea trout.
There's a fair body of research that shows, as Tups noted, the rainbow gene pool naturally includes a yellow skin pigment option. Possibly this is related to why there is such a thing as the high Sierra golden trout of California. The West Virginia mutant (Farmer Dave's hatchery freak name is as good a term as any) was discovered in 1954ish by a hatchery staffer and was one of those fish you sometimes see that is part normal color and part yellow. The staff kept it and named it Camo (short for camouflage). The West Va. statehood centennial was a few years off and Camo, it turned out, was able to produce full yellow offspring. The yellow trout we're introduced in 1963 and called the West Virginia Centennial Golden trout. This is all spelled out in one of the old WVa state fishing publications that can be found online. Read about it a few years back when I got curious about the creatures.
Pennsylvania had been screwing around with novelty trout for years, most notably tigers and to a lesser degree splake. Splake aren't all that much different from brook trout when you stock them in the 12 inch range. Tigers are kind of cool looking, but one with that dull hatchery color goes right on the stringer without a second look. Pa Fish Comm (pre boat) bought some WVa Goldens but the WVa conditions were 1-- new name. 2--cross the breeders with full rainbows (not sure why). So the Pa version became palomino, after the golden horse, I guess.
Flash forward a few years and Maryland starts stocking the yellow beasts.
Also sometime in the past two or three decades a yellow rainbow strain became part of the Pacific coast stocking regimen (Washington State, Oregon, Northern California) and they call it the lightning trout. I've read conflicting stories. One says it was derived separately from a mutant in possibly Oregon(?). The other says the lightning trout is essentially a WVa golden crossed with a rainbow (like the palomino).
Be on the lookout: the next big mutant rainbow strain on the horizon is the so-called blue trout. This is not to be confused with the localized southern strain of Arctic char once found in Maine and New Hampshire and known as blue back trout. These are supposedly sky blue rainbows. My cousin saw one cruising around in Yellow Breeches Creek last summer.
Fascinating though I find them, I've caught two Goldens in my 55 years. They're kind of like busty women in a crowded bar from back in my youth. Worth a cast or two, but their primary value, as noted earlier in the thread, is keeping the other guys occupied while you pursue the real catch of the day.
