One of the biggest problems with olefin is the fact that it is almost waterproof. This combined with 400+ psi. causes the cleaning solution and water to travel all the way through the backing.
This is the number one cause of browning in commercial cleaning.
Lower your pressure and depend on your chemistry and massive agitation like the Versa
CRB unit to suspend the soil before your wand ever touches the fiber.
I recommend using
Chemspec Fission, boosted with BioSolv and Energizer to help breakdown and emulsify those greasy oils and soils and finish with Optimal rinse to stop any wicking concerns.
If it is the traffic lane gray you are concerned with, this is nothing more than a major change in light reflection (which cannot be corrected completely) due to the matting and crushing that occurs quickly in olefin because of it's lack of resiliency.
I have always said that olefin comes pre matted, pre crushed and pre uglied for you because it takes very little time for it to occur