I found the definitive article from the 4/5/1954 Chicago Tribune. Referring to the 4th:
...yesterday announced a new regular grade gasoline "with a difference you can see."
...said it had colored the product a "distinctive purple" to identify it as the gasoline with the highest octane rating for regular grade in the company's 65 year history.

So, I guess I was off on the dates and apologize for that. Now the Torch & Oval sign makes sense.