I recommend that you recolour using a shade of colour from the colour pallet:
Colours: Edit colours.
Or, you can take another sprite, paste it next to the first one and take the colours of off that using the colours picker from lightest to darkest.
My favourite one out of these is Raquaza.
The outline may also need colouring, for example your Mewtwo still has a grey outline.
There is also another program you can get for free called Paint.net. That makes it much easier to recolour as you can just hold down shift and use the paint bucket tool on 0% to colour all of the coresponding colours on the sprite. It is very much like paint, just with more features.
They are definatley not bad for a first try, but I think you need to work on the colours and the outline. Otherwise, great job!
- ZD