It's a package based on
turtlesim simulator for ROS adding some extra functionalities. The idea of this project is keep the traditional funcionalities of the tutlesim and, on top of it, add more funtionalities so others can use this helpfull tool to teach more advanced topics in mobile robots. The code was build from the original code.
To the original features, there is the Turtlesim Wiki page with a really good documentation and a lot of tutorials.
It's a sensor that get the color ahead the turtle, similar to a range_sensor. Instead of measure the distance, given a certain distance, this topic gives you the RGB values of the pixel in that distance. The diference from the turtleX/color_sensor in the original
turtlesimis, this topic gives you the RGB color underneath the turtle, not ahead.