When I was about ten, a meddlesome adult told me that "blindman's bluff" should be
"blindman's buff.
The wordbook I am reading says "bluff" in seventeenth century mant "blindfod", and
that blinkers on horses were called "bluffs"
On the Internet, the two spellings are used to mean the same thing.
Have any of you got a theory to explain how "blindman's buff came into use?
Outside of just ignorance?

Fragonard did a painting sometime between 1775 and 1780, the English title of which is Blindman's Buff. Then there's this piece:

James Gillray (British, 1757–1815)
Blindmans Buff – or – Too Many for John Bull
Hand-colored etching, published by Hannah Humphrey, June 12, 1795

I'd never heard of the buff variant. It makes me think of nekkiditity.

Dear Soarteye: You've got it! Blindman's buff is the game played on a nudist colony!!

It makes me think of nekkiditity.

What's with the extra syllable there, Sparteye?

Extra syllable is from fantasy of being groped in the game.

I don't think Sparteye used an extra syllable.

Naked = nekkid (or however she spelled it)

noun form = nekkidity

Stupid --> noun form --> stupidity

I'd say she was on linguistically solid ground.

Look again, Dub. Nekkiditity.

Omigosh! Sparteye, that was a rather risqué spelling, wasn't it?

Thanks, Faldage, the ever-observant along with the ever-observant Miss Anna.

Myself, I've never heard the bluff variety before.

Grew-up-in-and-around-New-York-City-area:

I've heard it both ways - "blind man's buff" and "blind man's bluff." I always assumed one was originally the "right" way, the other an innocent mispronunciation on the part of some child many years ago, maybe several hundred. The meaning wasn't altered any; ultimately the change diffused out and was incorporated into the the common parlance as totally equivalent. By now the two are interchangeable.

(Note the scrupulous avoidance of suggesting which one is "correct" ! )

I've never heard the bluff variety before

Likewise - which goes a teeny little way to suggesting this could be a US variant.

I think I'd assumed the "buff" to be the bumping up against people the "blindman" does - as in buffeting .

M-W's etymology of buffet is interesting:

Etymology: Middle English, from Old French, diminutive of buffe blow
Date: 13th century
1 : a blow especially with the hand
2 : something that strikes with telling force

OED2 supports the buffet interpretation, giving bluff as an *early spelling variant:

bllind-man's-buff Also 6-7 blindman-buff(e, (-buffet, -bough, -bluff,) 7-9 blindman's-buff. [f.
BLIND-MAN + BUFF = buffet, blow, stroke.]

1. A game in which one player is blindfolded, and tries to catch and identify any one of the others, who, on their part, push him about, and make sport with him.

1600 ROWLANDS Let. Humours Blood iv. 64 At hot-cockles, leape-frogge, or blindman-buffe. 1628 GAULE Pract. The. (1629) 231 Others make him [Christ] no better then their Pastime, at no more discreet a Sport then Childs, or Fooles Blind-man-Buffet: Prophecie vnto us, who is he that smote thee? 1634 J. TAYLOR (Water-P.) Gt. Eater Kent, Gregorie Dawson, an English-man, devised the unmatchable mystery of Blind-man-buffe. 1696 Month. Mercury VII. 55 They oblig'd him to play with 'em at Blindman-Buff. 1766 GOLDSM. Vic. W. xi, Mr. Burchell..set the boys and girls to blindman's buff. 1866 R. CHAMBERS Ess. Ser. I. 186 The whole parlour put into disorder by blind man's buff.

2. fig.

1590 Three Lords Lond., Ile to my stall; Love, Lucre, Conscience, blindman buffe to you all. 1643 BRAMHALL Serpent Salve §1 We desire to see what they have done, before we go to blindman's buffet one with another. 1648 C. WALKER Hist. Indep. I. 55 Me thinks..we are compelled to play at blind-man-bough for our lives. 1837 CARLYLE Fr. Rev. I. VI. iii. 278 Government by Blind-man's-buff.

I had never heard blindman's "buff" until this thread, and I ain't bluffing.