How to make a shape the same colour as the background

Hello friends, I wanted to try to remake the fall guys loading screen and I wanted to make the circle the same colour as the background as it expands from the centre of the screen. I also don't want the background to be visible through the circle. I've tried different blending modes and layer styles but I none of them were what I wanted :p. 

I am very new to AE but thank you for the help in advance.