than a plain yellow based on photos I saw but I wasn't sure until I found a reference confirming that and the reason why:

"CSX2000’s first public appearance was at the 1962 New York Auto Show in April. The Cobra was painted a pearlescent yellow because Shelby was advised that color looked best under fluorescent lights. CSX2000 would be repainted several times over in its function as the sole factory demonstrator in an effort to convince customers and the automotive press that the production line was humming along."

Quote is from this article -> Link

Glad I bought the pearl paint for this project even though it's not a small block car. At least it will have some tieback to Shelby history.