Miles or operating hours, it is a moot point with me.
You may remember the old reliable Nalcool 2000 product was a dark red in color. That was due to phenolphthalein, IIRC. When the glycol oxidation caused the pH to drop below about 8, the product cleared up to a colorless or light yellow liquid, indicating it was time to change.
Nowadays, the colors are, I guess, just there to warn the consumer that he should stay with the product that the car producer supplied.
Hype reigns supreme with some of these products and their marketing.