My health potions are green and poisons are red

Crap fantasy is still fantasy. Had a great time coming up with bad fantasy stories in my childhood when I knew nothing about good writing. Art is what you make it.

A clearer way to phrase it might be "there are no rules for the genre of fantasy". An individual world needs self-contained rules, yes, but just because Tolkien's Dwarves have beards regardless of gender doesn't mean that your Dwarves need to be the same.

To write good Fantasy (of SciFi), you have to go through a process called “World Building”

I think this is more implying that you don't have to work from the same framework for every fantasy world. Not everything has to be set in Arthurian Medieval Times with Crusader-Era social sensibilities. The menagerie of mythical creatures isn't a prerequisite or delimiter (dragons / unicorns / etc are not a requirement nor are robots / cthulhoid horrors / woolly mammoths disallowed). You need internal consistency (to a degree) but you aren't forced to adhere / omit any genre trope.

I would say, at an absolute bare minimum, you need some kind of fantastical or supernatural element to make it "Fantasy" as opposed to "Historical Fiction" or "Science Fiction" or some other category of fictional prose. Although, the genre of "Magical Realism" does make even that distinction a bit fuzzy.

many literature teachers / professors don’t even know about the idea of World Building

You don't necessary need to go through the whole work of World Building if you're just banging out a short story or novella. Even serial writers don't necessarily bother going deep on the background material until they feel the need to expand the scope of the setting. I mean, look at the Star Wars setting. George Lucas didn't have Jabba the Hutt defined as a big slug monster until the third movie. In the original film, there was a cut scene in which Han confronts Jabba, who was just a be-feathered chubby gangster.

If you're just spitballing or cranking out bits of fiction in brief, World Building can be superfluous. A story that takes place entirely in a single house over the course of a long weekend doesn't need the kind of scaffolding that a Long Walk to Mordor requires.

Also the important rule here is everything not explained to be different is assumed to be the same as our understanding of the real world.

Rules for fantasy writers.

For a post centered on reading, the actual comprehension of what is being said in this thread is poor.

Toss a lighted match into the growing puddle.

Match goes out.

Nah this one is easy.

If it's green and sparkly, it's a good thing. If it's green and bubbly, it's a bad thing.

Purple: Magic??

Green: Life/death??

Red: Life/fire??

Blue: Magic/cold??

Honestly the only colour I don't feel uncertain about is orange, that's always bad.

Also on the topic of health potions, a great piece of advice I once heard was that if your players are in a foreign land, remove health potions. Give them health biscuits and watch them reconcile with God.

Or radiation perhaps?

That's a roguelike convention. Potion colors are randomized. Runes/scrolls usually arent.

Pixel dungeon does the same thing, you don't know when you start a run what any color potion does. So they're randomized.

FWIW, potions are drugs.

DM: Roll a Vibe Check

Player: I rolled Dark Green

DM: Ooohhh...

My vibe is slightly hurt with a hint of mental damage

Why should your fantasy game be limited by something like “health”.

One way of escalating drama and tension is by injuring a main character. The scene in Terminator 2, where Sarah Connor has to knock the T-1000 into the blast furnace with consecutive shotgun blasts, isn't nearly as cool without her doing it with a wound in her arm. Frodo collapsing from exhaustion gives us the incredible moment of Samwise shouldering him and carrying the guy, ring and all, up the slope of Mt. Doom. Tinkerbell fading away after hearing "I don't believe in fairies" is what gets the audience on their feet applauding her by the end of the third act.

And particularly for folks invested in the coolness of their characters, some conflicts are much more fun when the outcome isn't anything either storyteller or player could have anticipated. A totally unexpected David v Goliath moment, where a scrawny guy fells a giant with a lucky shot, will be the kind of story people talk about for years - whether David or Goliath or both are PCs.

what do you mean? electricity is purple

There is (was?) an electric power provider in Germany by the name of Yellow. Their whole marketing was "electricity is yellow!"

Electricity is yellow.
Blue would be water.

What game would actually use blue?

The pulp is from fruit, right? The pulp is from fruit, right!?

Granted.

Anthrax the Destroyer is how hiding among stuffed animals.

I love the possibility of having a red/green colorblind character and having to roll to hopefully pick the right potion when they both health potion and poison in their bag.

Also you need to consistently break conventions once you do it or you really screw with people and make a shitty world.

In Overwatch, healing is consistently represented by the color yellow. Mercy's beam, Ana's darts, Moira's piss, Soldier's healyboo, etc. Making Lucio's speed aura yellow and healing aura green would be visually confusing

Because his default coloring is green and yellow I'd guess

Then you are an undead