ColorOS Recovery Image is the easiest way to restore Stock ROM back easily. There will be new CWM and TWRP Recovery image for R5 soon. And after flashing that, the original ColorOS recovery is wiped out. To bring the device back to its original stage you will need official ColorOS Recovery that can be downloaded from here. The file size is around 10.4MB. To flash this stock recovery you have to install Minimal ADB Fastboot Tool on a Windows based pc. The Stock ROM can be restored through this tool. You can check out theis video for full restore process.