There was only one time Malachi had caught sight of a dot in the sky with his unique vision, and it also happened to be a coloured one.
Colour orange, to be precise.
Malachi couldn't say he knew a lot about his ability or even what the colours he could see with his unique vision truly signified, but he could almost bet his money on what the orange dot in the sky represented.
Based on the events that occurred in the past, Malachi knew that whatever was on the dot's side was something strong. He had seen orange a few times now in several crystal hearts to know it represented higher strength.
Malachi just didn't know the identity of the orange dot because, just like monsters, humans like him, his son, and Yuki's daughter all had crystal hearts. This meant that the range of what Malachi's eyes could currently fixate on in his vision could potentially be a human.
However, that was too much optimism. The apocalypse wasn't so kind all the time.