Can you refresh gazebo when you load through ROS?

I have a urdf model that I have loaded with:

roslaunch my_robot world.launch


I noticed that I gave the wrong color to a part of the robot. I have made changes. Is there a command to run to refresh gazebo from roslaunch? I have been quitting everything every time I make a change and I feel it is too much of RAM usage and slower.

It depends. If you're spawning the robot at runtime, either through the spawn_model service or from the Gazebo model database, then you can just just remove the robot from the simulation (click it and hit the <Delete> key), edit the model file and load it again. If it's directly included in the world file, then as far as I can find, no, you cannot reload it without restarting Gazebo.