Brian, what have you done?
Occasionally I am asked about this. What are all the small patches of brown or purple grass?? The question is only asked in winter...for good reason. Turfgrass will give a purple hue for one of two reasons. One, a nutrient deficiency, specifically phosphorous. Second, a cold temperature response. The nutrient deficiency is highly unlikely because even if I applied no phosphorous, the plant would still acquire it via the soil/ rainfall or the like.
Before I explain the cold temperature response, let me take a step back and give you a brief agronomy lesson. The greens at HCC are comprised of Penn A4 Creeping Bentgrass. It was developed at Penn State University. Penn A4 is simply the variety, with the species remaining bentgrass. For comparison, in gardening, the Tardiva Hydrangea is the old, trusty standby, with newer varieties hitting the market with different color flowers or sizes etc. Sometimes you might see a white flower on an otherwise blue flowering species. This is very similar to what's occurring above.
The A series of bentgrasses were selected and reproduced from an original stand of Penncross creeping bentgrass, a variety that dates back to 1952, developed and Penn State. All grasses and plant species in general will segregate over time and will revert back to the parent material. This is why brand new greens are always so pristine and uniform and as they age, the become "patchy." In the case of Penn A4, we start seeing some of those Penncross parent plants come out. One specifically, is a variety called Penn Lu bentgrass. Penn Lu was one of the 3 varieties that cross pollinated to create Penncross. Again, Penn A4 is a mutation of Penncross.
The good news is, once the temps warm, the purple disappears and the turf again becomes uniform.