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That looks like it might be flea dirt. If you put rubbing alcohol on flea dirt, it will turn from black to reddish. Fleas spend about 80-90% of their time off the pet, so it isn't unusual you wouldn't see them. Have you treated the environment?
Also, fleas will live and reproduce inside a vacuum cleaner. Is it a bagless cleaner? Placing moth balls inside the vacuum will kill them in there.
Fleas can live under furniture and along baseboards so vacuuming alone usually isn't enough. You usually have to use sprays or bombs, or if you want to go more natural, use Borax (check http://www.boraxforfleas.com/) or diatomaceous earth https://www.diatomaceousearth.com/natural-flea-control-for-cats/).
Regarding things other than fleas, some types of dermatitis can produce flaking, but that is more often white or beige versus black or brown. Giving regular baths with a good moisturizer such as oatmeal certainly should do no harm.
And fleas are sneaky buggers.....they can jump on, suck some blood, take a poop (flea dirt) and jump back off before you know it. :-)
We might be getting to the root of our problem. "Flea dirt" is black, not white. Black = flea dirt/poop. White = dandruff/flakes of dry skin, for which the oatmeal bathing and essential fatty acid skin supplements can help. And one last note: you cannot see flea eggs or larvae with the naked eye, they are microscopic.
Flea larvae are about 2.5mm, or less than a tenth of an inch, and eggs are about a fifth of that size. If you can spot them, you've got good eyes. :-)
The skin doesn't dry out if you are using a moisturizing shampoo such as oatmeal or aloe. I don't usually recommend lotions on pet's skin because I think it tends to block the pores.
Not sure about why the white flakes turn brown with the alcohol wipes, sorry.