Nicotine content in natural leaf increases from the bottom of the stalk to the top. Nicotine varies by seasonal weather. Nicotine varies by date of topping--earlier topping results in higher nicotine than later topping. Leaf that is primed at a more mature stage will have higher nicotine content. Nicotine varies somewhat by curing method and aging, but not by a lot.
Average nicotine content varies by tobacco variety (ranging from ~0.5 mg/gram of cured leaf to ~50 mg/gram of cured leaf.) Nicotine content of most commonly grown varieties ranges between 1 mg/gram of cured leaf to ~6 mg/gram of cured leaf. The nicotine content noted in the GRIN Observations often does not reflect what you will see when you grow that variety.
As for relating nicotine content to the descriptive terms used by marketeers of commercial tobacco products, there is no correlation.
A safe bet is that for a single variety, darker leaf is higher in nicotine than lighter-colored leaf.
Bob