Sorry, stickers in a non-technical term. Now that I know a little more, let me try again.
It sounds like you want a full color image in the background.
However, you want the user to see only an entire screen in black and white.
Then the user interacts, removing portions of the screen to show a colored portion of the far background.
If that is what you want to achieve, here is one way to assemble your assets to achieve it:
Make a full screen color background. (Background1)
Make an identical black and white image. (Background2) This layer will be displayed *on top* of the full color background. But it needs more done to it than being made black & white. You will need to (using a paint program) cut transparent holes in it (fill the parts to be removed with transparency). The holes are exactly the pieces you want the user to remove. Don’t throw out the black and white parts of the holes though. You will need those to display on top of the black and white…
Save the cut out black and white “holes” cut from background 2 (“stickers”). Your app will need to load and display these (what I called “stickers”) in exactly the spots needed to totally hide the colored image (hides parts of background1 that show).
Now that the display is set up, you would need to put event listeners on each sticker to detect when the user touched it, and then call more code to drag it around, delete it or whatever your app calls for. When the sticker is moved, it will reveal the transparent hole in background2, which background 1 is visible through.
Another way to do it is to have 1 background, mostly black and white, except the area where the holes are.
Those area you can make color, and cover them with a black and white sticker. (no two backgrounds, just one this way). If you display this background as is, it will look like the final image if the user removed all the stickers. In this case, you make the stickers black and white (so when displayed on top of background, everything looks black and white).
Not sure of everything you want to do though, so I have no idea which method is best for your app. At this point, if you display background2 on top of background 1 it will appear as if the user had removed everything you wanted.