I made this logo, but I want to flatten it so that it's always the same no matter what the background color is. How do I do this? It consists of three ovals with the "overlay" blending mode. It's made in Sketch. Thanks!
No need to flatten. Insert a piece of 50% grey (R=G=B=128) behind it with blending mode normal. A perfectly fitting piece can be made as boolean union of the copies of those shapes.