Ah yes, I can see why you might think that.
But when I find something that surprises me and proves my assumptions wrong, I like to delve a bit deeper into it and share the results. It's mostly curiosity...

I only know of diesel sold under lower tax rates being dyed red to prevent those with access to it using it in anything other than agricultural equipment and ships. There are many diesel powered vehicles, including passenger cars, over here, so you can understand the temptation.
Nowadays it's been further restricted to use in boats and ships (excluding those for recreational/leisure use) only.

As you can see on my photo, the tank is almost pristine, even after 25 years. In the seam of the intank fuel filter (the "sock") I found some hairs and sand grains, which probably fell in while filling the tank. No gunk, no rust... and still the fuel filter under the car clearly had a job to do.

It's been suggested that thet grey stuff might be carbon worn off the brushes in the pumps, but that seems like way too much to come from just the brushes.

About the ethanol, by law, petrol has contained at least 5% ethanol for years now. And there is a shift towards 10% ethanol (E10), but some engines (mostly directly injected ones) cannot be run on it. Volvo is one of the few manufacturers that say running E10 is fine in most models from 1976 on, most other manufacturers like to stick around 2000.