How to Install Third Party Blocks (like RGB block) In EV3 Mindstorms

1. You need to have your third party block in your computer.
   1. If you want to install the classic Mindcub3r block, download ColorSensorRGBzip-v1.00.zip to your computer.
   2. If you want to install the enhanced RGB block from ODFL, download this block on your computer.
2. Extract the file from this archive (if it is a .zip file. Otherwise, skip this step).
   On a computer running Windows, find the file in Windows Explorer, click with the right mouse button and select Extract all…
3. Start the LEGO MINDSTORMS EV3 software and create a new, empty project.
4. Select the Tools menu and then Block Import.
   

5. In the Block Import and Export dialog, select Browse.

6. Find the file, which has .ev3b extension on your computer and Open it.

7. Select the .ev3b file from Select Blocks to Import and then select Import.

8. To complete the installation, close the dialogs and exit from LEGO MINDSTORMS EV3 software.
   
   

Source:

How to build MindCub3r for LEGO MINDSTORMS EV3: http://mindcuber.com/mindcub3r/mindcub3r.html