Not all casings come with fan filter and to reduce dust intake you need products like the Silverstone FF124-E Fan Filter.
The Silverstone FF124-E Fan Filter has magnets and this makes it easy to apply for casings where the intake is at the rear, commonly found on systems that run with AIO cooler.
Ironically this doesn’t work well on even some of the casings from Silverstone where the rear grille for the fan isn’t of a flat plane. Mounting it from within the casing is often not possible as well as the long screws of AIO often are enough to accommodate casing thickness but not the thickness of a fan grille as such.
In the end the fan filter is useful but with limitations, and you’ll need to know the limitations before buying. As for the colors, it’s now limited to Black/Red and Black/Green combo, of which again is not only another limitation but it’s also not exactly a nice looking color combo.
Retailing at around 7 USD over at Amazon, I like it that it’s magnetic and works fine as long as the conditions are met. It works best if you can just magnetically place it at the rear of system setups where the rear is an intake, or use it with the front intakes that does not come with filter as the mounting screw is able to hold both the filter and the fan in place.
More details at the official product page.