Considering that you only need to fill parts with the colour, you could do it all with only one sprite and tint effect on the parts. Original, colourless parts should be maked in white/grey colours like in child colourings.
However even if there were no plugins and effects. You still could simply change colours with different sprites, but where's fun in that?
Once the painting is ends with some little confirmation process game should proove that player has used the right colours to fulfill image's parts. You can make it with a private variable or without it.
You can have this confirmation process going on it's own when all parts are filled with a colour or you can give the confirmation button which player free to press in any time or once again when parts are filled with a colour.
To easy development you can separate game process on three stages:
Stage 1: Example (Big example is showing, already coloured big parts and then tint-effect is slowly going to 0 (Like changing opacity, but you do it with the effect). Going next to Stage 2!
Stage 2: Painting (Let player see a miniature and the colouring instruments when example is gone. Starting to fill white/grey parts with a colour. Once finished starting our confirmation process. Going to Stage 3!)
Stage 3: Confirmation (Game confirmates big parts true colour and then finishing a game process kicking player forward to the next level. If player failed the confirmation you can start level from the beginning (Stage 1) or just make amends and go through confirmation process again)
Rojohound's plugin is great and you should try it, but I doubt it will help in this project unless you need to actually draw pictures. With a time it can be done as well.
Wish you luck!