Hello, have a look at my photo's Vicster. I just took a snap of my chilli plant with green, black & red chilli's all on the same plant. Hopefully yours are in the dark midway colour section to turning red so all should be well.
In the unlikely event they are failing ( hope not ) let me know details if that's convenient but I feel sure your chilli's are just getting hot hot hot !!

Hi, thanks for that, have just looked at the plants again and there is one red chilli on one of them!

excellent !!!

Chillies can be green, yellow, orange, purple, black and even white depending on the variety.