FYI the yellow started with the CJ engines. Prior to the CJ the dip stick tubes were bk in 68 on 390 and 428 PI (Shelby).
Not sure if it was "started" with the CJ but will agree that the "color coding" of the tubes to the application started in 69 from what I found so far. Do have original examples of yellow being used on 69 390 C6's - then we have the FMX and other examples.
But we're getting off thread a little
Guess we can always move it if we all want to go down that rabbit hole