I can't give a total answer to this, but I can make some observations which may help. Firstly, the habit of depicting angels with colourful wings has never actually been fully abandoned. Here is a mural from 17th century Italy. Here is a French painting of the 19th century, and a 20th century Irish stained glass window. At the same time, here is Giotto's fresco of the crucifixion from around 1300, which depicts quite plain-winged angels. Personally, I suspect that local traditions and the artist's own imagination and resources were a large part of it, rather than set tradition. William Blake, for example sometimes depicts angels with iridescent wings, sometimes with white. You can see a similiar range of approaches with non-Christian winged figures as well, for example Cupid. See an 18th century British take on Cupid and Psyche, and a 17th century Dutch rendering. The colours of angels wings are (to my knowledge) not explicitly mentioned in the bible, though some artists have, I believe, associated certain meanings with various colours. For instance, there is a certain tradition of depicting the seraphim wearing red, and possibly with red wings. I unfortunately don't have a copy of Hall's Dictionary of Subjects and Symbols in Art to hand, but that might be a good place to start looking for more information.