Digital Color Meter
macOS includes a colour picker:
- Open Digital Color Meter from Applications → Utilities.
- Move the pointer over the colour you want.
- Choose View → Display Values → As Hexadecimal to see hex.
- Press ⇧ ⌘ C to copy the value as text.
Press ⌘ L to lock the position while you copy.
The system colour panel
In apps with a colour well, such as Pages or Keynote, the colours panel has an eyedropper to pick from anywhere on screen.
Convert it
Copied a hex colour and need RGB, or the other way round? NotchMind, which I make, recognizes a copied colour like #0A84FF or rgb(10, 132, 255) and offers Preview Color and Convert Color. Its Developer Tools page converts too. See developer tools, or do it by hand with hex to RGB.
NotchMind