The following is the modification on the previous code to add the color blue:

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

    <material name="blue">
        <color rgba="0 0 0.5 1" />
    </material>

    <link name="base_link">
        <visual>
            <geometry>
                <box size="0.6 0.4 0.2" />
            </geometry>
            <origin xyz="0 0 0.1" rpy="0 0 0" />
            <material name="blue" />
        </visual>
    </link>
</robot>

Explanation of the code:

<material name="blue"> This defines a material named "blue".

The <color> tag specifies the color using the RGBA format:

• R: Red component.
• G: Green component.
• B: Blue component.
• A: Alpha (transparency) component (1 = fully opaque).

Why Use <material name="blue" /> in <visual>?

The <material> tag defines a reusable material, and <material name="blue" /> applies this material to the specific visual element.

• Purpose of Re-usability:
  • By defining the material once (as "blue"), it can be applied to multiple links or visual elements without redefining the color every time.
  • This makes the URDF file more compact and easier to maintain.