Early on in the series, Delenn (played by Mira Furlan) put herself into a kind of cocoon and came out looking significantly more human than Minbari. The in-universe explanation was that she wanted to be closer to the humans, or something like that. I'm wondering if there's an out-of-universe explanation for why the writers would put that in - maybe the actress disliked all of the makeup or something like that.
She certainly hated the makeup, describing it in interviews and on her blog as very masculine and unpleasant to wear:
During the pilot when the last remnants of my vanity were crushed by the masculine alien make up I had to wear, it was Andreas who urged me to remember that all acting began with masks in ancient Greece. When I was complaining of being hot under the blazing California sun, it was Andreas who told me to remember the old peasant women in "the old country", covered from head to toe by loads of thick black cloth in the middle of the summer. "The sweat cools you down", he would say and take a long drag from his cigarette between his rubbery G-Kar lips.
She also (according to the show's senior prosthetic and makeup designer; Greg Aronowitz) pushed, right from the start to be able to play her character with substantially less makeup, with increasing success each successive season:
She could not believe that the production would fly her all the way to America, completely cover her face in an androgynous make-up, give her a male voice, and hide her eyes behind black lenses. We were asked to leave the trailer, and when they let us back in, Delenn was to be a flesh colored female alien with eyes that looked like Mira Furlan’s!
I have to give her credit, there are very few actors that can take a stand like that and have so much be changed to accommodate their view of the character! True fans of the show will recognize Mira’s continuous push to have Delenn be more human, as with each passing season, there was less make up, more hair, and my alien antler design merely became a tiara!
Purely as a matter of interest, although her original makeup was rather more dramatic (and her new makeup hardly any better) the reality is that her post-human makeup actually took rather longer to put on, due to the need to interweave the bone-spur into her long hair.