Well said, it happens with most colors, even Ti clear.
And over the years, Oakley might have tweaked the process with the chemicals involved in the lens cooking and so many other factors involved. Thats why, while most lens will look the same in a particular iridium, you will see variations sometimes.
Here is one thought...California is a real bitch about EPA regulations and the SCAQMD (air quality mgmnt) requirements, so maybe over the years, the fumes, VOC, or resulting exhuast from the process have caused the need to change certain aspects of what goes into the processing, therefore resulting in a bit of variation between batches...Could be a learning curve if you will, between perfecting the right process with changes...May be way off, may be right on, but a thought. I know that the state, epa, and scaqmd have caused a lot of headache for auto paint, hair products (yes, Joico Spiker hair gel/glue has fallen prey to the VOC requirements and therefore is a much weaker product), and just about anything that could result in pollution or contamination of the air.