Want to adjust color rendering with Pyhthon "MaterialColor"

It does not work, example from Rhino Python:

import rhinoscriptsyntax as rs
obj = rs.GetObject(“Select object”)
if obj:
index = rs.ObjectMaterialIndex(obj)
if index>-1:
rs.MaterialColor( index, (127, 255, 191) )

As material from selected object is default then nothing happened, this is correct. When material is not default, the color is changed to (127, 255, 191), this is correct and displayed also in the rendering. But the in the properties page the object material properties do not change.

Do i something wrong or is this not possible, to change the material color?

( skills beginner in Python and RhinoPython )

I see where/my mistake is in thinking.

Need to create first a material before I can change for example the color or other property.

Thanks for the tip