While I don’t normally take requests, an apparent exception to that rule is that when my mom asks me about the origins of a phrase, I must comply. At least if I know what’s good for me. Last week, my dear mother asked me for more information on the origins of the phrase tickled pink ‘immensely pleased’. On that basis, I’m tickled pink to do so. I assumed there would be an obvious answer online within about 30 seconds. Not so much.
The good news is that the sense is well-agreed-upon: when you tickle someone intensely, their skin pinks up as you torture them horribly, and thus to be tickled pink is to be tickled until you’re pink. I haven’t found any source that disagrees with that etymology, at least, and it makes a lot of sense (unlike the earlier, more hyperbolic, and more gruesome tickled to death). The date and place of origin are where it gets tricky.
My go-to person for idioms is Michael Quinion, whose World Wide Words has covered just about everything. But the only mention there was a casual allusion in the entry for blue murder. So no help there.
The OED mentions tickled pink in its entry under tickle. But that only takes it back to 1922 and doesn’t really provide much more context.
The Online Etymology Dictionary dates it from 1909 but provides no additional information.
The Ngram for ‘tickled pink’ is interesting – it confirms the 1909-ish date (we can see the actual result here, from a play called ‘Hicks at College’. It shows big spikes starting in 1917 and 1939 – so perhaps connections to the world wars, in terms of increasing its popularity – then a sharp drop-off after WWII and a new increase starting in the late 70s.
But I know that if it’s showing up in a play in 1909, with no sign of being marked and with no explanation, that it must be earlier. So a-hunting I will go.
Google Books doesn’t have anything other than an erroneous 1867 hit (a misdating of a conference proceedings). Most of the other standard databases came up empty. But then I found this article from 1900 in the New York Sun of July 15, 1900, using the Library of Congress Chronicling America project:
So now we’re back to the turn of the century in New York City, but we still have a mystery in that the phrase doesn’t attract any attention and is just passed over without remark. I went off to some more specialized subscription and local newspaper archives and did a bit more searching, but I came up empty there.
There’s always more work to do, but for now all we can say is that it probably dates to the last decade of the 19th century (if it were much earlier, you’d think it would have come up somewhere in the masses of printed text from that period) and that its sense really hasn’t changed much in the past century. So I’m tickled pink to have taken it back this far, but rubbed the wrong way now that I’m stuck.
Glossographia 
The Alphi Phi Quarterly, Volume 26 (1914) claims it’s “conservative Boston slang”, which is interestingly specific.
Also, for note, the 1911 Roget’s thesaurus includes it.
I saw that piece from the Alpha Phi Quarterly – I tend to read ‘conservative Boston slang’ in a college magazine as ‘one of my conservative parents uses this term’, which to me, fits with it being actually coined in the 1890s, but not necessarily in Boston.
I hadn’t looked in Roget’s – that’s a good catch! If it was sufficiently circulating by 1911 to be included (by which time we only have a dozen or so print examples) it was probably more common than it first appears.
There are a couple of other things in the OED that might be relevant:
1. The relevant sense of tickle (`please’/`titillate’) is quite old; the OED’s earliest example of it is from Chaucer (ca. 1386). So it’s just the addition of the intensifier pink that’s the innovation here. (This is implicit in the contrast you draw between “tickled pink” and “tickled to death,” but I think it’s worth pointing out explicitly.)
2. Pink as an intensifier or superlative had also already been around for quite a while; the OED glosses this sense as `the “flower”, or finest example of excellence; the embodied perfection (of some good quality)’ and gives an example from Shakespeare (1592).
3. “Strike me pink!” as `an exclamation of astonishment or indignation’ seems to have emerged at around the same time as “tickled pink”; the OED’s earliest example of it is from E. Nesbit (1902). In its literal meaning, this would be the same kind of resultative as “tickled pink” (since striking someone also causes the blood to rush to the skin).
Right, of course your points are entirely correct. As for ‘strike me pink’, that’s interesting and I hadn’t heard it before, but I agree that it is very similar semantically and if it’s in the OED at 1902, we can almost certainly antedate it. Actually, we definitely can. Just a moment’s checking reveals that it has a number of Google Books results starting in the early 1890s. These, however, all seem to be British, as opposed to ‘tickle me pink’, whose earliest instances are all American. So it’s certainly a very interesting correlation, but also creates another mystery.