在gazebo当中不用再设置颜色了，因为完全可以使用urdf的设置

<robot name="base" xmlns:xacro="http://wiki.ros.org/wiki/xacro">
  <xacro:property name="PI" value="3.1415926"/><!--定义一个变量PI，后边用来调用的-->
  <xacro:property name="base_footprint_radius" value="0.001"/>
  <xacro:property name="base_radius" value="0.1"/>
  <xacro:property name="base_length" value="0.08"/>
  <xacro:property name="ground_clearance" value="0.015"/>
  <xacro:property name="base_mass" value="0.5"/>
  <link name="base_footprint">
    <visual>
      <geometry>
          <sphere radius="${base_footprint_radius}"/>
      </geometry>
    </visual>
  </link>
  <link name="base">
    <visual>
      <geometry>
        <cylinder radius="${base_radius}" length="${base_length}"/>
      </geometry>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <material name="red">
        <color rgba="1 0 0.0 1"/>
      </material>
    </visual>
    <collision>
      <geometry>
        <cylinder radius="${base_radius}" length="${base_length}"/>
      </geometry>
      <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
    </collision>
    <xacro:cylinder_inertial m="${base_mass}" r="${base_radius}" h="${base_length}"/>
  </link>
  <joint name="base2base_footprint" type="fixed">
    <parent link="base_footprint"/>
    <child link="base"/>
    <origin xyz="0 0 ${ground_clearance+base_length/2}"/>
  </joint>
  <!--
  <gazebo reference="base">
    <material>
      Gazebo/Blue
    </material>
  </gazebo>
  -->
  <xacro:property name="wheel_radius" value="0.0325"/>
  <xacro:property name="wheel_length" value="0.015"/>
  <xacro:property name="wheel_m" value="0.05"/>
  <xacro:macro name="add_wheel" params="name flag">
    <link name="${name}_wheel">
      <visual>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_length}"/>
        </geometry>
        <origin xyz="0.0 0.0 0.0" rpy="${PI/2} 0 0"/>
        <material name="green">
          <color rgba="0 1 0.0 1"/>
        </material>
      </visual>
      <collision>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_length}"/>
        </geometry>
        <origin xyz="0.0 0.0 0.0" rpy="${PI/2} 0.0 0.0"/>
      </collision>
      <xacro:cylinder_inertial m="${wheel_m}" r="${wheel_radius}" h="${wheel_length}"/>
    </link>
    <joint name="${name}_wheel2base" type="continuous">
      <parent link="base"/>
      <child link="${name}_wheel"/>
      <origin xyz="0 ${flag*base_radius} ${-(ground_clearance+base_length/2-wheel_radius)}"/>
      <axis xyz="0 1 0"/>
    </joint>
    <!--
    <gazebo reference="${name}_wheel">
      <material>
        Gazebo/Blue
      </material>
    </gazebo>
    -->
  </xacro:macro>
  <xacro:add_wheel name="left" flag="1"/>
  <xacro:add_wheel name="right" flag="-1"/>
  <xacro:property name="holder_wheel_radius" value="0.0075"/>
  <xacro:property name="holder_wheel_m" value="0.03"/>
  <xacro:macro name="add_holder_wheel" params="name flag">
    <link name="${name}_wheel">
      <visual>
        <geometry>
            <sphere radius="${holder_wheel_radius}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0.0 0.0 0.0"/>
        <material name="blue">
        <color rgba="0 0 1.0 1"/>
         </material>
      </visual>
      <collision>
        <geometry>
            <sphere radius="${holder_wheel_radius}"/>
        </geometry>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
      </collision>
      <xacro:sphere_inertial m="${holder_wheel_m}" r="${holder_wheel_radius}"/>
    </link>
    <joint name="${name}_wheel2base" type="continuous">
      <parent link="base"/>
      <child link="${name}_wheel"/>
      <origin xyz="${flag*(base_radius-holder_wheel_radius)} 0 ${-(base_length/2+ground_clearance/2)}"/>
      <axis xyz="1 1 1"/>
    </joint>
<!--    <gazebo reference="${name}_wheel">
      <material>
        Gazebo/Blue
      </material>
    </gazebo>
-->
  </xacro:macro>
  <xacro:add_holder_wheel name="front" flag="1"/>
  <xacro:add_holder_wheel name="back" flag="-1"/>
</robot>

这个代码完全使用了urdf自己的颜色rgba，没有使用<gazebo>内的<material>标签，事实证明即使添加一个<material>标签，也不会有用，所以这样设计更加方便。算是进化了

请诸位放心，一切都在掌控之中哈哈