what does ink mean?

What exactly do they mean by “blue” ink in the context of “blue or black ink”? Is that light blue or dark blue? Who’s judgment ultimately determines if the ink is “blue” enough? And how do they differentiate a really dark blue from black? If they say blue or black, a really dark blue could be both, depending on who you ask. Is blue or black intended to be mutually exclusive?

haha, heel veel succes!