I do like selective colouring. I certainly like the Duck.
The two practice picks, you have done well, and used the technique well.
But, I just don't like the two pictures you used (sorry).
I guess on the flowers one, why that flower? If it were a tulip in a field of daisies, then it might mean more.
The one with the boats, looks to me like it is a grey picture, with a bit of colour. those are just my views though. Perhaps if the hull of the police boat was greyer it would be better?
However, what is probably more important than all of that, is do YOU like the outcome, are you happy with how the pictures look? You /have/ performed the technique well, it is something I am particularly useless at and cannot get right myself, so who am I to speak!