My favorites are orange isopod morphs.
I always liked the black morph of leopards and jaguars. But I have never seen those in person, only on TV.
As for in-person, I remember my fascination as a kid, discovering that chicory – normally a blue flower – has a rare pink morph and a rare white morph. But you asked about animals, so that doesn’t really count.
During a road trip, I visited Olney, Illinois specifically to see the white morph eastern gray squirrels for which that town is known. And then on another road trip, I was in Vancouver, British Columbia, and discovered the black morph eastern gray squirrel – which is an introduced species in that West Coast city.
Blue morphs in frogs are especially cool, AKA Axanthism
I have yet to find one myself, but I know there are quite a few records here on INaturalist :)
every so often I used to see C. atrox with a pattern that vanishe ddown the last 1/3rd or so of their bodies. That looked awesome.
I’ve also seen some Texas long nose snakes with no red (years ago before I owned a camera). They were out near the rural panhandle town my now-wife was living in at the time. Haven’t seen any like that out there in years though
If wildtype counts as a morph, then copperheads are up there at the top for me, especially the super light colored ones that almost look white.
In terms of morphs I’ve personally seen, I really love the red-striped Rough Earthsnakes(Haldea striatula), I’ve only found one or two individuals, but it really puts a different spin on a somewhat common species.
Since most of the time I gander at insects, I am obviously biased toward Lepidoptera. Also, technically all insects fall under the Kingdom Animalia, so the inclusion of insects in the title is somewhat of a pleonasm. But to get back to the original question, I like what I call the “eye-outline” morph in Biston betularia and all of its associated subspecies. The funny thing is I had no idea that this feature even existed on the Peppered Moth until it was conspicuous on a specimen in North America.
The original observation https://www.inaturalist.org/observations/63008871 by @cyrusli.
Another majestic example of Insect coloration would be Attacus atlas ryukyuensis (if the genomic data still supports this designation). This insect is probably the closest thing to a real life Mothra (unless someone decides to inject it with radiation).
Original website: http://blog.livedoor.jp/lucanus/archives/52089106.html. (This is not my own picture)
Oops sometimes my brain just shuts off.