I've read interviews with GM engineers who were discussing the programs they have to compensate for temperature, humidity, paint load (amount of paint in the vat) and the specific characteristics of each color. I know from experience that each specific color has slightly different characteristics due to the materials used to create the color (pigments). Each specific paint has a spec sheet that describes how to thin it based on temp and humidity.
In the thread regarding the paint finish petition it was mentioned that they blame the excessive OP (all current mass produced cars have some OP, every single one of them regardless the price) on the new to 2014/15 composite panels and their porosity. That would seem counter intuitive if all the OP is in the clear but not really. Since this is a wet/wet application (the base coat has not cured prior to the clear being applied) it's reasonable to think that the panel porosity is leaving the paint surface inconsistent (some areas drier than others as more solvents have been absorbed by the panel). The paint surface may be smooth but the clear will OP if some of the paint has a higher content of solvent.
The running fix (bandaid) is to use a double coat of primer. The long term fix is to work with the vendor to produce a panel with lower porosity. They commented that the roof, hood and trunk are CF which has very little porosity so that's why you see less OP on those parts. Not no OP, just less.