USD DataAlgo : Fix valueTypeName() for Color4f[Vector]Data

We weren't specifying the "Color" role, which meant we couldn't round-trip shaders with Color4f parameters. They were being written as `float4` and then not loaded at all.

Author: johnhaddon

contrib/IECoreUSD/src/IECoreUSD/DataAlgo.cpp

@@ -412,6 +412,21 @@ struct VtValueTypeNameFromData
 		return s.FindType( TfType::Find<typename CortexTypeTraits<Imath::Color3<T>>::USDType>(), g_color );
 	}
 
+	template<typename T>
+	SdfValueTypeName operator()( const IECore::TypedData<vector<Imath::Color4<T>>> *data ) const
+	{
+		using ArrayType = VtArray<typename CortexTypeTraits<Imath::Color4<T>>::USDType>;
+		const auto &s = SdfSchema::GetInstance();
+		return s.FindType( TfType::Find<ArrayType>(), g_color );
+	}
+
+	template<typename T>
+	SdfValueTypeName operator()( const IECore::TypedData<Imath::Color4<T>> *data ) const
+	{
+		const auto &s = SdfSchema::GetInstance();
+		return s.FindType( TfType::Find<typename CortexTypeTraits<Imath::Color4<T>>::USDType>(), g_color );
+	}
+
 	// Generic
 
 	template<typename T>

contrib/IECoreUSD/test/IECoreUSD/USDSceneTest.py

@@ -3047,5 +3047,34 @@ def testWriteDoubleSidedAttribute( self ) :
 					doubleSided
 				)
 
+	def testColor4fShaderParameter( self ) :
+
+		network = IECoreScene.ShaderNetwork(
+			shaders = {
+				"output" : IECoreScene.Shader(
+					"mySurface", "surface",
+					{
+						"color4fParameter" : imath.Color4f( 1, 2, 3, 4 ),
+						"color4fArrayParameter" : IECore.Color4fVectorData( [
+							imath.Color4f( 1, 2, 3, 4 ),
+							imath.Color4f( 5, 6, 7, 8 ),
+						] ),
+					}
+				),
+			},
+			output = "output"
+		)
+
+		fileName = os.path.join( self.temporaryDirectory(), "shader.usda" )
+		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Write )
+		child = root.createChild( "child" )
+		child.writeAttribute( "surface", network, 0 )
+
+		del child, root
+
+		root = IECoreScene.SceneInterface.create( fileName, IECore.IndexedIO.OpenMode.Read )
+		child = root.child( "child" )
+		self.assertEqual( child.readAttribute( "surface", 0 ), network )
+
 if __name__ == "__main__":
 	unittest.main()