You can fill individual images, since they are pygame Surfaces.
First, what I would do is I would put something like this after defining the leaf's x/y:
leaf.image = img1
Then, I would create a color variable called transparent:
transparent = (0, 0, 0, 0)
The first 3 numbers, as you might know, represent RGB color values. The last number is the alpha (transparency) value of a color. 0 is completely invisible.
Finally, I would add this code to make the leaf completely transparent:
leaf.image.fill(transparent)
This makes the leaf transparent without making every other image in your window disappear. Hope this helped!