Changing an existing material with code

I have a mesh that is loaded from a j3o file converted from a blender model.
The standard model has a green material but I want some variations of it to be black or otherwise.

The below code works fine, but I find it wasteful to create a new material when there is one already. Can I just getChild() or getMaterial() to find the material, and set its color to black, instead of replacing it with a new one?

I found setMaterial methods as below, but no getMaterial or such.
private void redress() {
Spatial apa = (Spatial) this.getChild(“Cylinder.0031”);

    Material mat = new Material(assetManager, "Common/MatDefs/Light/Lighting.j3md");
    mat.setColor("Diffuse", ColorRGBA.Black);
    ParticleEmitter spark = (ParticleEmitter)this.getChild("spark");

Only geometries have a getMaterial (). I normally create my own method to traverse a spatial for the first geometry (in most cases theres only 1 anyways), and return the material of it. In your case, if you have the child already, then just cast it to a geometry