Welcome to the Cake Decorators Q&A

I have made some royal icing leaves and flowers and have left them overnight and they still remain soft.
I don’t know why they haven’t hardened? I made the icing stiff enough and piped onto sellophaine with a little stork marg on. Also, I coloured icing with blue colour paste. This has happened before and had to throw everything away. Would like some advice on what I might be doing wrong.

It’s possible the colour affected the consistency. Some dark colours can break the icing or cause it to remain soft and tacky. There could be other reasons like humidity or if you over greased the cellophane or if you added too much colour in all at once.
If you google ‘problems with royal icing’ you’ll find lost of information why this happens and how to avoid it happening again.