I tried to imagine Master Aryon dressed casual and practical for traveling.
The inspiration was the note in his Dwemer Museum, recommending the visitor come back often as he is always acquiring new artifacts on his travels. This suggests that he is not above a bit of adventuring and wandering around in random holes in the ground (similar to what Steen does in her free time). Of course, he would not be all decked out in his full Telvanni raiment whilst doing so. Hence this drab and rugged little number: ready to weather the most violent ash storm, yet comfortable and flexible for mobility.
Inversely, I always draw Steen in her worn old traveling clothes, without much finery (and I’m uncreative with outfits), so I tried to imagine what Archmagistress Steen would like like in full-on Telvanni finery. I wanted it to be super ostentatious and extravagant. I’m still playing around with the ideas, clearly, but at least she doesn’t look like she just came back from a week-long mountaineering expedition. Maybe Aryon pleaded with her to try to not wear something covered in dirt to a big important function, so she threw this together. I mean, she was a low-born nightblade, so… something something new money. I don’t know.