Created attachment 164578 [details] Visual representation of the issue When you choose one of the offered accent colors in System Settings, it seems like the color is slightly translucent. If light theme is chosen, the selection background and other elements that use that color are pale, if dark theme is chosen, they are somewhat darker. A good way to see the difference is to choose a custom accent color and then also manually edit a color scheme, changing elements like Selection Background and Focus Decoration to the same color.
Indeed, the actual color you choose can be modified in various places where it's used. This is something we eventually plan to move away from (where practical), but it's something that's intended at the moment.