I have created a heat map in QGIS and have successfully exported it as a Geotif file. I exported the file as a Rendered Image to include my classifications and colors. However when I pull the data into Tile Mill or Map Box, all of the pixels with "No Data" get colored as white or black. I have tired setting the "No Data" to be 100% transparent in QGIS but this did not change anything. I want the white/black space to be excluded.