Quote Originally Posted by WhiteArchmage View Post
The ALC questline needs a certain potion and/or dust to show the color of a person's soul, so while regular people can do it, they need external aid for it. It certainly foreshadowed that different people have different soul signatures, but isn't something that regular non-Echo blessed can do on a whim.
I'm still not entirely sure if the particular concoction in that ALC questline (50-60, if anyone was wondering) showed the actual objective colour of a person's soul, or if it shows a colour that happened to be unique to each person.

For example, using the dust, the colour of the WoL's soul is "blue". I don't know if that's just the colour as shown by the dust itself, or if Hythlodaeus would agree "yes, that soul colour is that exact shade of blue". In other words, whether the dust is fingerprinting (showing the actual form of the mark) or Luminol (showing the presence of the mark, but using its own output).