Mojave has a nice dark theme, but to change it you need to go click trough multiple screens to change the theme. Darksome lets you switch with a mouse click.
Display Maestro
This menu bar app gives you full control over attached displays, allowing the use of all available resolutions and bit depths.
Display Menu
Quickly check for available resolutions, refresh rates, or retina capability on any of your internal or externally connected displays and projectors. Switch between aspect ratios or turn on mirroring with a single click.
DisplayBuddy
DisplayBuddy lets you control your external displays: Setting brightness, contrast, and volume from your Mac’s menu bar.
Displays
Click on Displays icon in the upper-right corner of your screen and choose your monitor resolution among all supported resolutions.
