Some things I find interesting.
 Hope you also do....
Modern US Postal History
A purple B stamp with a purple cancel.  WOW... it's purple heaven :)

The 18¢ rate period was a short one, beginning March 22, 1981 and ending a short seven months later October 31st.

The purple machine cancel is an EKU "ALWAYS USE ZIP CODE" from Seattle Washington on May 11, 1981.