Have a look at these 2 pictures. The one on the right is Cleo's locket in series 1 which you can easily see the Blue Stone. The one on the left is Cleo is series 3 and i am certain that the stone on that locket is Clear?!
I do apologise for the picture not being very clear, but it is the best picture i could find.
Please leave your comments about this, as i am sure i am not the only person to spot this. Lets find out if and why Cleo has Emma's locket...
Thank you, please help me ;)