Magma volscheme gradient

[AlexandreDeCamargo]

I am trying to pass a MAGMA gradient scheme in order to colour my 3D plot:

view.addVolumetricData(cube_data, "cube", {'isoval': isoval, 'smoothness': 10, 'opacity':.7, 'voldata': mep_data, 'volformat': "cube", 'volscheme': {'gradient':'ROYGB', 'min':-1., 'max':1.}})

But I can't find any references for gradient colours scheme.