No?
Let id0 be the function on single letters that maps A to 0, B to 1, C to 2, ..., Z to 25.
Then Proxima's half-rule states: For each letter c that is not A, a koan that contains exactly n >= 3 copies of c [and nothing else, EDIT Simon after namida's reply] is buddha iff id0(c) divides n. Equivalently, that koan is budda iff there exists a natural number m with id0(c) * m = n.
The marked koans violate this, because the koan BBB is black. (Everything of the form B{n} with n >= 3 appers to be black.) Also, namida mentioned there exist two letters, such that koans consisting only of copies of that letter are always black.
Noes, I can't read properly. n divides id0(c) is the claim. That would make B and C the two letters that make only black same-letter koans.
-- Simon