More back-story and a picture of the envelope can be seen at The Sneeze.
CHARLES M. SCHULZ
NUMBER ONE SNOOPY PLACE
SANTA ROSA, CALIF. 98401
December 23, 1986
I can't believe that you are so ready to leap in with your criticism.
Fifteen years ago, when the strip was drawn, I believe there was only one black in the National Hockey League. Does pointing out this fact make the strip racist?
Charles M. Schulz