Answers:
最后,通过这段代码,更改图层颜色对我来说是可行的:
QgsMapLayerRegistry.instance().addMapLayer(self.vlayer)
symbols = self.vrlayer.rendererV2().symbols()
symbol = symbols[0]
symbol.setColor(QtGui.QColor.fromRgb(50,50,250))
qgis.utils.iface.mapCanvas().refresh()
qgis.utils.iface.legendInterface().refreshLayerSymbology(self.vlayer)
您还必须重新加载MapCanvas和“图层”面板。