This is the Lego EV3 color sensor. It is similar to the Lego NXT color sensor, but they have combined a light sensor in it. The Ev3 is more square and thin so it can fit in tight spaces. In the NXT color sensor you did not have a cross hole option while in the Ev3 kit you have it on the bottom. The cross hole option allows you to capture motion. You can even build around frames with the Ev3 color sensor. This is going to enhance the building experience. This is a change they made to all the EV3 sensors. They have also improved the actual function of the sensor. Instead of detecting 6 colors like the NXT, you detect 8 in the Ev3. That helps you in programing the sensor. There are now multiple modes that you can use. They are the reflected light and ambient light mode. Reflected light mode lets the robot detect the change in reflect of the color. Ambient light lets the color sensor absorb and detect what color it is facing. You still have the two circular connectors on the bottom on the sensor. I think that Lego made Ev3 better with the sensors as you do not have to do a lot to program them.
Here is a color sensor tutorial for you:
Summary of Tutorial:
In this video the robot keeps going forward until the color sensor detects a color. When it does this, the robot is supposed to move back. I would recommend to do this multiple times to check if the color sensor is working.