bloomhjelm
Ooooh.... I like this. Not saying I'm correct either but this is how I describe the traits.
Patches- I call it bicolor but in my notes will continue to describe it as 80% dark purple throat with fading white centralized tips. I usually give the color ratio in percentages and then note how the color change looks (sharp or fading).
Tips- also tips
Striation- I note the side of the petal and also use striation. Striated reverse.
Concentration - I see why you would use this term. I've floated a few around in my head but haven't landed on the perfect term. I currently use the phrase "filtered pigment layer" as is reminds me of graphic design terms when an artist can layer color on an image at different transparencies.
Iridescence - Diamond dust, because Ted pointed out the Iris community used that term to describe the petal surface that redirects light in a sparkling manner. When another established plant group has a term that can be applied to dahlias, I tend to defer to their definition as an effort to maintain cohesiveness among the horticulture industry.