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