How to add label to point without marker displaying in QGIS with python

I'm using a python script to manipulate the display of shapefiles in QGis.

My code basically selects an active layer and sets a field as the label of the point. Like this:

layer = qgis.utils.iface.activeLayer()
label = QgsPalLayerSettings()
label.readFromLayer(layer)
label.enabled = True
label.fieldName = 'objnam'
label.placement= QgsPalLayerSettings.OverPoint
label.setDataDefinedProperty(QgsPalLayerSettings.Size,True,True,'8','') 
label.writeToLayer(layer)
QgsMapLayerRegistry.instance().addMapLayers([layer])

This give's me the following result:

I would like to add code so that the coloured marker will not be visible. I've tried adding the following above my code in attempt to make the marker transparent:

renderer = layer.rendererV2()
symbol = QgsFillSymbolV2.createSimple({'style':'solid', 'color': '255,255,255,0', 'style_border':'no'})
renderer.setSymbol(symbol)

But this seems to do nothing. I have a feeling that I misunderstand how the symbol layer works. Any help or guidance is welcomed.

Answer

Size should be 0. Just add this parameter to the params dictionary like below:

symbol = QgsFillSymbolV2.createSimple({'size':'0'})