In the resizing step, click Customize then Color. Color-in your design with the materials you want. At the bottom of the coloring page, you can enter the size of your design and it gives you the material list.

To access the material list later, load the saved colored design and go to the Coloring tool (from where you can enter the size, click Customize, then Color).

Your design should be black lines on a white background. If it's not, convert it. Shapes must have no gaps in their lines. You can use the Designer to complete lines.

Applying other tools (e.g., crop) to a colored design will prevent changing its coloring or getting the materials list later. So make sure to finish making design changes before coloring.