Twain did have red hair; don't know about this "apparent
self-report" of brown hair.
An unfinished article of mine, for a scholarly Twain
journal, makes note of Twain's red hair--a point which the
esteemed editor corroborated in his critique, though the
fact is "seldom mentioned and...not widely known." In fact,
he suggested this as a possible area for further study. I
may yet re-work my article into one about Twain and his
"Red-Headed League" of friends, which included the famed
sculptor Augustus Saint-Gaudens.
The red-hair issue is further corroborated by William Dean
Howells in _My Mark Twain_, who commented on his friend's
"splended shock of red hair." Howells is certainly an authority.
(An aside: Last I knew, the wax museum at the Haunted House
on Hill Street, in Hannibal, had Twain incorrectly sporting
dark brown eyes! Twain's daughter, Susy, wrote that "Papa
always wares [sic] grey to match his hair and eyes.")
There are those out there on the Forum with electronic
Search capabilities that I lack; but that our hero's head
was of the firey variety, in both the literal and the
figurative sense, is without question.
Mary Leah Christmas