For some reason(this is really bizzare) in the subscreen editor, when making a new triforce piece, the graphic that applies isn't transparent at all. In other words, if the tile I'm using for triforce piece has bright green for a trans. color, the piece on the subscreen has a bright green background that should be transparent.
Subscreen Triforce
Perhaps you need to check the "Transparent" field under the "Attributes" tab...