The Collaborative International Dictionary of English v.0.48:

ocher mutation \o"cher mu"tation\ n. [A humorous variation on
   the term amber mutation.] (Microbiology, Molecular biology)
   A mutation in which the base sequence of one of the codons in
   the messenger RNA has been converted to UAA. Such a mutation
   may be conditionally suppressed, as can an amber mutation,
   by the presence of a special transfer RNA. -- ocher mutant,
   n.
   [PJC] Ocherous