Create an interactive coloring application where users can color in outlined images.

Main Features:
- Image Selection Screen:
  - Display small, easy-to-navigate thumbnails of provided images.
  - Images are clickable for selection.
- Coloring Screen:
  - Show the selected image in full-screen vertically.
  - Top-left controls include:
    - 'Back' button with a confirmation dialog: 'Are you sure you want to go back?'
    - 'Save' button to download the colored image as a PNG.
  - Top-right control includes:
    - A large red circle indicating the currently selected color (default is bright blue).
    - Clicking the color circle opens a full-screen palette with 24 vibrant color options arranged as small circles.
- Coloring Interaction:
  - Detect image area boundaries for color filling.
  - Users can click/tap within an area to fill it with the selected color.

Best Practices:
- Ensure an intuitive UI with clearly labeled buttons.
- Optimize image processing for quick boundary detection during coloring.
- Provide a fluid experience when toggling between color selection and painting. This application encourages creativity and offers a simple, engaging, and satisfying experience for digital coloring enthusiasts.

Create a simple interactive coloring application:
First screen:
- Display thumbnails of the provided images:
  1. https://img.freepik.com/free-vector/hand-drawn-zoo-animals-illustration_23-2151199715.jpg
  2. https://img.freepik.com/free-vector/hand-drawn-zoo-animals-illustration_23-2151199718.jpg
  3. https://img.freepik.com/premium-vector/lion-giraffe-hand-drawn_185029-508.jpg
  4. https://img.freepik.com/free-vector/hand-drawn-owl-outline-illustration_23-2149277379.jpg
  5. https://img.freepik.com/free-vector/hand-drawn-fox-outline-illustration_23-2149272718.jpg
  6. https://img.freepik.com/free-vector/hand-drawn-lion-outline-illustration_23-2149285355.jpg
  7. https://img.freepik.com/free-vector/hand-drawn-penguin-outline-illustration_23-2150582038.jpg
  8. https://img.freepik.com/free-vector/animal-doodle-outline-cute-giraffe_1308-81895.jpg

- Thumbnails should be small and easy to navigate.

After selecting an image:
- Display the chosen image full-screen vertically.
- Top-left corner:
  - "Back" button: returns to image selection after confirmation dialog.
  - "Save" button: downloads the colored image.
- Top-right corner:
  - Large red circle indicating the current selected color (default is bright blue).
  - On clicking the circle, display a fullscreen palette with 24 vibrant color options arranged as small circles. After selecting a color, close the palette.

Coloring interaction:
- Detect boundaries of image areas.
- On click/tap within boundaries, fill the area with the selected color.

Q: How should users confirm when they click the 'Back' button?
A: A simple 'Are you sure you want to go back?' prompt.

Q: What specific file format should the colored image be saved as?
A: PNG format.