I went digging around for images of the felt backing under the tiles, as
I noticed on the images of the tile ding from orbit it appears to be
black in color:
http://a52.g.akamaitech.net/f/52/827...einspct_02.jpg
Images of the tiles being applied to the Shuttle though show that the
surface they are applied to appears to be white:
http://www.dfrc.nasa.gov/Newsroom/X-...ages/tiles.jpg
....are each of the tiles backed with black felt, and is this then
secured down to a white felt that is attached to the exterior skin of
the Shuttle?

Pat