@Override
    protected void initFilter(AssetManager manager, RenderManager renderManager, ViewPort vp, int w, int h) {
        material = new Material(manager, "Common/MatDefs/Post/Overlay.j3md");
        material.setColor("Color", color);
    }
sets the color

@param color the desired color (default=(1,1,1,1), alias created)
jme3-effects/src/main/java/com/jme3/post/filters/ColorOverlayFilter.java