Differentiation for game design/balance reasons most likely.
Just think about how annoying some gods could be if every indicator looked the same.
In this case, if they were the same, it’d be a matter of “is that an old Clio ult in the wall or is she exiting it?”
Yep, we wanted to ensure that portal was only used in places where it was clearly her ultimate or in context with an animation (dying, recalling) that could provide the context it wasn't a gameplay element.
For entering/exiting the wall we wanted it to be visually distinct so that was clear for enemies to know her intentions and that if they see a portal in that scenario they know it is dangerous. Functionally she also doesn't use the portals to 'travel' so the theme of her becoming ghostly might have been lost if they were used.
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