Black mold around fuel door
 

OK, I searched as best I could in the various threads. Could not find any info on this problem, so here goes.

I wash my Snow White car infrequently (it's cold in Georgia this winter!)
And I notice that around the fuel door that is a splattering of what appears to be black mold. And even more inside the door, and around the filler neck.
Windex will get it off, but it returns. So.....

Is it caused by:
1. A fungus on the paint/wax/cleaner that I use?
2. Something in this gov't mandated gasohol (I try to get 'real' gasoline, but sometimes....) like the corn whiskey ?
3. A chemical?
4. Something coming up the fuel cavity drain?
5. Or some unknown Stuttgart gremlin playing with my head?

So, knowing the cause would be nice..... But...

What can I do to clean 100% and PREVENT the black stuff from returning?:

You might try washing it off with a strong detergent and then apply a good coat of wax. See what happens.

I've noticed this also and only in the past few years since 10% Ethanol was mandated, on cars I've owned for 20 years. It has to be from Ethanol fuel as nothing else has changed.

Bleach water works to clean, spray mold remover might keep it away.

Dirt...
 

I have noticed this on my car, too. I suspect that rather than mold, what you are seeing is road dirt, composed of soot, dirt, oil residue, brake and tire dust and anything else around, that is kicked up into an aerosol when it rains, and flows into the fuel door. It accumulates there because that part of the vehicle isn't washed very often. I cleaned it off my car with car wash soap. I suspect that a good coating of wax would make it easier to remove. Might also be worthwhile to confirm that the fuel 'box' drains are working. Cars here in SoCal (where it doesn't rain very often) don't have much of a problem with this.

What I did
 

OK, forgot to answer with my 'fix'.
I got a long shaft 3/8 drive and took off the 2 bolts holding the fuel door.
Real simple, except the spring needs to be wiggled to get the socket seated/in firmly.
Then poured a little water down the drain hole to test. Working fine.
Then used several types of cleaners, but some old 3-M stuff used to remove scuffs/mars/bug/tar finally worked. (Took the spring out to get in the cracks.) Used an old toothbrush (careful, that can melt!)
Once done, I got out my can of good old paste wax. Swirled it all around and one the clean backside of the door. Once done, got rid of excess, then simply re-bolted the door to the car. Took a few tries to get perfect alignment.

Done ! A success story !!!!!!!

I thought I was the only one who's picky with the fuel filler recess being clean!