So if you've watched Season 5, then you know that both Lotor and Allura's marks glowed. That's because they both have The Mark of The Chosen. But Coran doesn't have it even though he's also Altean. I think that's because it only happens to Alteans who have some sort of alchemic ability in their blood. It could also be because Lotor and Allura both have white hair and Coran has orange hair. Plus Alfor also had white hair, so he also must've had the ability because Allura has it. Unless she got it from her mother, who also could've had the ability as well.

I could be wrong, but this is just my theory.