There are a lot of transparency effects in macOS these days. You can see it twice in the Finder window above: the colors from the desktop wallpaper show through the left sidebar, and the pictures I’m scrolling past bleed through the top of the window. You can even see this while scrolling.
The effects are kind of neat, but potentially distracting, and in some cases they can slow down your Mac—so if you want to speed up your Mac, you might try turning them off.
Thankfully, they’re quick to disable, albeit a little buried. First, open the System Preferences and head to the Accessibility panel.
From here, click the “Display” option in the left panel, then click the “Reduce Transparency” option.
The transparency will be gone immediately.
As you can see, the sidebar and the top of the window are now unremarkable. Enjoy not remarking on them.