The lock, frame, and home options can be very difficult to see when using a reference image with high contrast.
If the center on the container is on a light spot, but the buttons fall on a dark spot, they become nearly invisible. (The opposite is also true)
I believe this has already been solved in a way that reduces overhead of checking pixel values. Just put a dark outline around light icons, as it seems to work great for subtitles.
Cheers