Have managed to side load App onto crystal sky, and it connects well, except video is in black and white. Photos record in colour.
Pity because it would be great.
Any comments welcome.

Hi，it sounds more like compatible issue. Crystalsky is not in the compatible device list. Thus the devices in the compatible list would be suggested to test if the video is still in black and white. Here is the link : https://www.ryzerobotics.com/tello/downloads.

Thanks. It is in colour on my phone, so  720p probably not useable on C Sky.