Sketch "Trim Transparent Pixels" is unselectable/greyed out


I am trying to export icon svgs to icomoon and am getting svgs with a huge artboard. I believe i need to select "Trim Transparent Pixels" checkbox on the artboard in Sketch but it is greyed out. I created a brand new project and it is still unselectable. Does anyone know how to enable this option/why it could be showing as unselectable

9/29/2015 3:40:00 PM

You should select Background Color and deselect Include in Export:
enter image description here

9/30/2015 4:12:00 AM

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