GM used PPG paint on the Reatta and other cars, the code in your trunk should be 81. According to GM's PPG paint code sheet it is listed as
GM Buick PPG - Bright Red - 3794
Code 81 - WA-8774
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C. F. Massie
Wichita, Kansas
"The Air Capital"
(Hawker/Beechcraft-Cessna-Bombardier/LearJet-Boeing)
89 Red/Tan Reatta