I'm trying mop n glow. Never thought of that!Its a combination of the product and the tire itself that leaches that brown coloration. From everything I've read, and my own experience, an approach that works well is:
Thoroughly clean the tires using a product called Bleche White. You can pick it up at almost any auto supply store. It will get the tires as clean as they can get and will prevent the 'brown' look that is common to certain tire brands. I'm currently running Nexxen tires and see this bown haze build up on the tires much more than I did when I was running Nittos or Toyos.
If you want a nice black tire, but without the oily look so many tire dressings have, try using Mop-and-Glo. Yes! I'm talking about floor cleaning product. Its costs almost nothing compared to tire dressing and leaves a dark black non-greasy looking finish that lasts for weeks.