Blending Modes Not Working

As you can see in these screen shots, I was trying to adjust the appearance of an existing video by adding a rectangle above it and then adjusting the blending mode of that rectangle's fill. No matter what blending mode I select, nothing happened-- the blend mode did not seem to affect the video's appearance at all.

Thanks for any help you can provide! Hopefully I'm missing something and this is simply user error, not a problem with After Effects.