Create a property node linked to the graph (right-click on the graph and select create property node), expand it to have two properties and make the first property the Active Y scale property, wire the index of the right hand Y scale to it (could be 0 or 1 if you have two). Now - the second property you need to set is the YScale.TextColor property which can be found as YScale->Marker Colors->Text Color in the properties menu (pops up if you click on the property node terminal). Wire a color value to that and you're there.
