applying material properties to named and unnamed visuals in a urdf

material_applied_to_named_visual.sdf

<sdf version='1.7'>
  <model name='urdf_gazebo_extension_test'>
    <link name='link1a'>
      <inertial>
        <pose>0 -1.5 0 -2.14159 0.141593 0.858407</pose>
        <mass>100</mass>
        <inertia>
          <ixx>2</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>3</iyy>
          <iyz>0</iyz>
          <izz>4</izz>
        </inertia>
      </inertial>
      <visual name='link1a_fixed_joint_lump__named_visual_visual'>
        <pose>0 -1.5 0 0 -0 0</pose>
        <geometry>
          <box>
            <size>0.2 3 0.2</size>
          </box>
        </geometry>
      </visual>
      <gravity>1</gravity>
      <velocity_decay/>
    </link>
  </model>
</sdf>

material_applied_to_named_visual.urdf

<?xml version="1.0" ?>
<robot name="urdf_gazebo_extension_test">

  <link name="link1a">
    <inertial>
      <mass value="100"/>
      <origin rpy="1 3 4" xyz="0 -1.5 0"/>
      <inertia ixx="2" ixy="0" ixz="0" iyy="3" iyz="0" izz="4"/>
    </inertial>
    <visual name="named_visual">
      <geometry>
        <box size="0.2 3.0 0.2"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 -1.5 0"/>
    </visual>
  </link>

  <gazebo reference="link1a">
    <visual>
      <material>
        <ambient>0 1 0 1.0</ambient>
      </material>
    </visual>
  </gazebo>

</robot> 

material_applied_to_unnamed_visual.sdf

<sdf version='1.7'>
  <model name='urdf_gazebo_extension_test'>
    <link name='link1a'>
      <inertial>
        <pose>0 -1.5 0 -2.14159 0.141593 0.858407</pose>
        <mass>100</mass>
        <inertia>
          <ixx>2</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>3</iyy>
          <iyz>0</iyz>
          <izz>4</izz>
        </inertia>
      </inertial>
      <visual name='link1a_visual'>
        <pose>0 -1.5 0 0 -0 0</pose>
        <geometry>
          <box>
            <size>0.2 3 0.2</size>
          </box>
        </geometry>
        <material>
          <ambient>0 1 0 1</ambient>
        </material>
      </visual>
      <gravity>1</gravity>
      <velocity_decay/>
    </link>
  </model>
</sdf>

material_applied_to_unnamed_visual.urdf

<?xml version="1.0" ?>
<robot name="urdf_gazebo_extension_test">

  <link name="link1a">
    <inertial>
      <mass value="100"/>
      <origin rpy="1 3 4" xyz="0 -1.5 0"/>
      <inertia ixx="2" ixy="0" ixz="0" iyy="3" iyz="0" izz="4"/>
    </inertial>
    <visual>
      <geometry>
        <box size="0.2 3.0 0.2"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 -1.5 0"/>
    </visual>
  </link>

  <gazebo reference="link1a">
    <visual>
      <material>
        <ambient>0 1 0 1.0</ambient>
      </material>
    </visual>
  </gazebo>

</robot>