It doesn’t matter which side of the antenna faces out if you are using the antenna on an interior wall.  We only suggest that if you are using your antenna in a window we suggest that you face the white side out because the white will reflect the sun’s rays where the black side will absorb them and cause the antenna to curl.  If you live in an extremely warm area you may want to secure all 4 corners of the antenna to the window you are using it in if possible.