Well, I have a bunch of lower-end black fans, some of them quite old, from before transparent cases were a thing. They're actually pretty much gray if I don't wipe them off.
Noctua's signature... brown-orange? Whatever that color is, it has the same issue. The blades are basically gray if I don't wipe them.
Haven't seen anybody start a gray craze, though. Though I have a grayish motorbike that also shows dust and dirt like nobody's business (it's a bike I use strictly on paved roads).
Silver is the ideal color for hiding dirt. I had a silver car once. Unless you drove it down a dirt road during a rainstorm, you basically never had to wash it.
If it were about performance and not marketing, they'd try to optimize for resistance to dust adhesion and resource consumption: energy, cost, durability, etc.
Why do you think they don't optimize for things like performance when they often win performance competitions against other vendors for both sound mitigation and airflow?
Do you know they have a specific high efficiency line?
Have you ever had a noctua fan fail where you think another vendor fan would not have?
I have them. They get dusty at about the same rate as a pure black fan (which also shows gray/brown dust quite easily). I need to clean mine about every 6-9 months to keep them looking good enough to "show off". I generally run a Winix HEPA filter in each room of my apartment.
I don't think matte white is worse than matte black in terms of showing dust. They both do.
It seems that common means something very different to you and I. Less than 5% of something is common? To me that sounds like the definition of uncommon!
Noctua's signature... brown-orange? Whatever that color is, it has the same issue. The blades are basically gray if I don't wipe them.
Haven't seen anybody start a gray craze, though. Though I have a grayish motorbike that also shows dust and dirt like nobody's business (it's a bike I use strictly on paved roads).