For years now, Apple has made transparency a part of the macOS interface, which has the effect of blending the menu bar into the background and making menus and some windows take on the background hue, as you can see on the left side of the illustration below. The effect is that each window on your Mac is like a piece of frosted glass, giving more of an impression that items are layered. For many people, transparency blurs the interface, making it harder to differentiate interface elements from the wallpaper. It also causes problems for screenshots meant for publication because the images end up with unrepresentative color levels. To prevent that from happening, open System Preferences > Accessibility > Display and select Reduce Transparency. It can be a significant difference, as you can see on the right side of the illustration below.
While you’re at it, if you have difficulty with seeing some things on your screen you can check the box for “Increase Contrast” which puts darker borders on most items. Do NOT, however, move the slider at the bottom for display contrast. Increased contrast sounds like a good idea, and it is in the upper checkbox, but anything other than normal on the slider makes the screen appear washed out.
(Featured image by Adam Engst)