DiffBot is an autonomous 2wd differential drive robot using ROS Noetic on a Raspberry Pi 4 B. With its SLAMTEC Lidar and the ROS Control hardware interface it's capable of navigating in an environment using the ROS Navigation stack and making use of SLAM algorithms to create maps of unknown environments.
Although the color of the tire is specified as black inside the wheel.urdf.xacro URDF, its shown in yellow inside Gazebo simulation:
Investigate why this happens. The motor Gazeb color is working correctly, only the tire color doesn't fit.