For such interactive actions you will have to access the 'synchronized copy' which every driver internally maintains of the global scene. Since a scene may get displayed by many drivers at the same time, this internal copy only reflects all changes due to user interaction / modifications.
private void button1_Click(object sender, EventArgs e) {
ilPanel_3D.GetCurrentScene().First<ILSurface>().Colormap = Colormaps.Summer;
ilPanel_3D.Refresh();
}
PS: no need to wait for two days the next time ... ! ;)
@Edit2: Actually, the update works just fine on the global scene also. But in order to broadcast the change to the ilPanel1 driver, you will have to add a call to Configure() at the end of your modifications. Configure can be called once for all changed nodes on one of their common parent nodes. So, you might simply call Configure() on the scene:
private void button1_Click(object sender, EventArgs e) {
ilPanel_3D.Scene.First<ILSurface>().Colormap = Colormaps.Summer;
ilPanel_3D.Scene.Configure();
ilPanel_3D.Refresh();
}