Does anyone know why they call it artifact colors? It creates a valid colorburst signal, so the colors are exactly as expected. It's high-resolution black-and-white imagery that's more of an artifact.
Guessing not knowledge but I expect it was called that from the accidental occurence of color on broadcast TV wben the image includes something with black-and-white stripes at the right spacing. So the name predates the intentional usage by the comphter system.
Because they're square waves and not proper modulated signals.
It's a specific technique where you deliberately modulate the signal so as to interfere with the color subcarrier. This can be used to produce colors that are otherwise not available.