Robot missing color and wheels fall halfway through plane

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When i load any urdf model robot into gazebo's empty world, the color of the robot is not displayed. Here is an example of one of the robots I which does not show up correctly:

I also noticed an issue where the robots wheels penetrate halfway through the plane of the world. I think it might be an issue of the position of my colliders for the wheels but I cannot be sure since I am new to urdf.

<?xml version="1.0"?>
<robot name="pioneer">
    <link name="base_link">
        <visual>
            <geometry>
                <box size="1 0.5 0.4"/>
            </geometry>
            <material name="red">
                <color rgba="1 0 0 1"/>     
            </material>
        </visual>
        <collision>
            <geometry>
                <box size="1 0.5 0.5"/>
            </geometry>

        </collision>
        <inertial>
            <mass value="10"/>
        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>

    </inertial>
    </link>


<link name="right_front_wheel">
    <visual>
    <geometry>
    <cylinder length="0.1" radius="0.15"/>
    </geometry>
        <material name="black">
            <color rgba="0 0 0 1"/>     
        </material>
    <origin rpy="1.6 0 0" xyz="-0.2 0 0"/>
    </visual>

    <collision>
    <geometry>
    <cylinder length="0.1" radius="0.16"/>  
    </geometry>

    </collision>

    <inertial>
            <mass value="10"/>
        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>

    </inertial>

</link>



<link name="left_front_wheel">
<visual>
<geometry>
<cylinder length="0.1" radius="0.15"/>
</geometry>
<material name="black"/>


<origin rpy="1.6 0 0" xyz="-0.2 0 0"/>
</visual>
<collision>
    <geometry>
    <cylinder length="0.1" radius="0.16"/>  
    </geometry>

    </collision>

    <inertial>
            <mass value="10"/>
        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>

    </inertial>
</link>



<link name="left_back_wheel">
<visual>
<geometry>
<cylinder length="0.1" radius="0.15"/>
</geometry>
<material name="black"/>


<origin rpy="1.6 0 0" xyz="-0.2 0 0"/>
</visual>

<collision>
    <geometry>
    <cylinder length="0.1" radius="0.16"/>  
    </geometry>

</collision>

<inertial>
            <mass value="10"/>
        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
</inertial>

</link>

<link name="top">

<visual>
<geometry>
<box size="1.3 0.8 0.1"/>
</geometry>
<material name="black"/>
<origin rpy="0 0 0" xyz="0 0 0"/>
</visual>

<collision>
    <geometry>
        <box size="1.3 0.8 0.1"/>
    </geometry>

</collision>
<inertial>
    <mass value="10"/>
    <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>

</inertial>

</link>



<link name="right_back_wheel">
<visual>
<geometry>
<cylinder length="0.1" radius="0.15"/>
</geometry>
<material name="black"/>        
<origin rpy="1.6 0 0" xyz="-0.2 0 0"/>

</visual>

<collision>
    <geometry>
    <cylinder length="0.1" radius="0.16"/>  
    </geometry>

</collision>

<inertial>
    <mass value="10"/>
    <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
</inertial>


</link>

<joint name="front_Left" type="fixed">
    <parent link="base_link"/>
    <child link="left_front_wheel"/>
    <origin xyz="0.5 -0.3 -0.25"/>
</joint>
<joint name="front_Right" type="fixed">
    <parent ...