Interesting article about the "Westernizing" (i.e. Whitening) of Ethiopian Orthodox Tewahedo Iconography. Historically this happened during times of agressive Roman Catholic and/or Coptic incursions into Ethiopian, a form of "Ecclesiastical Colonialism" if you will.
"In ancient times saints were painted as brown or black people, like, for example, in the Debrebirhan Selassie church, Gondar. Yet, the influence of western art is becoming more apparent. Nowadays it is common to see a Michael Angelo, Leonardo Da Vinci or Sandro Botticelli style of painting."
I would bet that it is coming first of all from church authorities who have an unspoken desire to cozy up to the Western churches and the Copts (for political and other reasons), although I would also imagine that it is part of a long, slow process of indoctrination amongst the laity as well. There is a fairly pronounced system of color prejudice/caste in Ethiopia with light skin being valued and dark skin being denigrated and I am sure this has something to do with it as well. I am not sure how far back in Ethiopian history this goes, but it is very well established at this point in history. Even amongst Beta Israel (Jews) in Israel, there is a division amongst "Red' and "Brown" Ethiopian Jews and "Black" Ethiopians, with the latter often coming from families that were enslaved by their fellow Ethiopians when they were still in Ethiopia. Seeing that saints and biblical figures in the oldest icons are depicted as darker complexioned, I would imagine that the color caste system was not as pronounced in ancient times. I suspect that the "divide and conquer" tactics of European and Egyptian interlopers encouraged this tendency. The Italians even tried to use slavery as a reason for their brutal, violent invasions of Ethiopia; you know, the "concern for human rights" that western occupiers always say they have when they want to occupy someone.