PowerPoint allows you to draw curves as lines, but it is harder to make fills under a curved line without resorting to actual data charts. Here is what I do: I use rectangular shapes to cut/shave a shape. See below. Notice that it is also possible to fill your custom shapes with images.

Draw a shape

Draw a shape

Position your knife

Position your knife

Use the "subtract" function to cut the shape

Use the "subtract" function to cut the shape

Horizontal knife

Horizontal knife

One more cut

One more cut

Fix the edges with format shape - edit shape - edit points

Fix the edges with format shape - edit shape - edit points

Add an image if you want

Add an image if you want