Watching TOS "Turnabout Introuder" right now, and I have to say, I reckon that Majel Barett looks far more attractive and alluring as a brunette than she does as a blonde, as she was throughout the rest of the run of TOS (barring "The Cage", of course).
Majel decided she wanted to finish TOS the way she started: as a brunette, but... I've been told that Chapel's wigs had a habit of being "borrowed" for functions away from the studio, and so here they were at the end of the series, with little change of there being a Season Four, and every Chapel wig had strangely vanished... again.
I love me some mousy brown Lwaxana. If you were going to do Lwaxana now she would come with purple streaks and her hair would be a a different shade of something every time you saw her. I think they should have glammed Lwaxana up more in dress and looks, to match the fabulous personality Majel gave her.