You know he actually did some front vocals for the group. In Shades of Grey he sings lead on the second first. Usually he did backing vocals, but in that song he did (well somewhat) a lead.
I never understood, though, why Mike Nesmith, even as a lead on some songs, never joined in backing with Peter, or Davy or even Micky. Another question, but back to topic yes its a shame another 60's musician passed on.