Scenario: Photo taken 8/19/09. Practice football field in Columbus Ohio. Mixed sward of Kentucky bluegrass, perennial ryegrass and rough bluegrass (Poa trivialis).

A football camp was held several weeks ago and the field was striped with turf paint and marked with crosses, rather than numbers. Primo Maxx was used in the paint to prolong the painted lines. Everywhere that was painted is now dark green.Green crosses and lines are especially visible in patches of light green Poa trivialis. The Poa trivialis is right on the brink of being dormant and will be straw-brown in the next day or two.
Upon closer inspection, the lines and crosses do not contain Poa trivialis. Only perennial ryegrass is in the lines. Something has selectively "taken out" the Poa trivialis.

Is it the paint or the Primo Maxx or a combination of both?

We have seen paint effects before where the painted areas contained more soil moisture and therefore the lines stayed green when the field went dormant. In this particular instance, the lined areas appeared dryer, but no differences were detected with the soil moisture sensor.
A few years ago, Dr. Dave Gardner and his graduate student Ben Wherely did research whereby they applied Primo Maxx to turf in shade and it had a detrimental effect on the Poa trivialis. So the Primo Maxx may possibly control Poa trivialis, especially when the Poa trivialis is stressed.

Ref: Gardner, D.S., and Wherley, B.G. (2005) Growth response of three turfgrass species to nitrogen and trinexapac-ethyl in shade. Hort Science Vol. 40 (6) 1911-1915