Apparently, several types exist. The high-end ones are the blue/black I was describing (Staedtler Mars Lumograph), while the black/yellow ones (Staedtler Noris)

Apparently, several types exist. The high-end ones are the blue/black I was describing (Staedtler Mars Lumograph), while the black/yellow ones (Staedtler Noris) are the most common ones.