This massive image modification removes colour profile information and adds an alpha channel. The first saves a little space, the second costs a little space. First is needed since SDL on OSX applies colour profile info which, while cool, is useless so long as the other theme colours are un-adjusted. Second is since we are apparently requiring full 32 bit surfaces now.

install(FILES
    Border.png
    Flake.png
    Girder.png
    horizont.png
    icon.png
    LandTex.png
    plant1.png
    plant2.png
    plant3.png
    plant4.png
    Sky.png
    theme.cfg
    horizont-lowres.png
    Sky-lowres.png
    DESTINATION ${SHAREPATH}Data/Themes/nature)