There's someone for everyone

I heard it‘s called Vitiligo

Heard...? Is this not common where you're from...?

There are places where this is common?
Second question. Genetically, does this mean that their children will definitely have it?

Can't say about the first question, but, while I haven't heard of any concrete proof of whether Vitiligo is genetic or hereditary, people who have it are a lot more likely to have children that develop the disease. It's not guaranteed, but odds are definitely not in their favour

I didn't even know it was a disease. I just figured it was a genetic mutation, I guess...

Well, honestly, there seems to be mixed research about it. I've seen it called a disease, a condition, a disorder, and a handful of other names. Research on it is incomplete, but a lot of people have started classifying it as an auto-immune disease/disorder, where the body is attacking it's own melanocytes-- which are the cells that produce the melanin that pigments our skin, hair, eyes, etc

In South Africa this is fairly common... I can't count the amount of people I know personally with this skin condition and walking down the street if you see someone with it you kinda just shrug it off... it isn't really a big deal....
Also I've never seen it passed down through generations... it seems to impact people randomly

*beautiful people are beautiful, and ugly people can be beautiful on the inside. Then there are just beautiful ugly people and ugly ugly people.

Beauty doesn’t last, and doesn’t determine one’s value. There’s nothing wrong with being ugly.

Is the converse true? Is there everything wrong with being beautiful?

No, only that beauty is not eternal. Your physical appearance should be a nonfactor, and someone's worth shouldn't be determined by a circumstance of birth