Color Picker For Ubuntu 19.10 (and later releases as well)

IMHO it is not very efficient to open Firefox to pick colors, at least I wouldn't do that, especially because you can implement Ubuntu native tricks like @Porcupine answer, which I'd like to expand, in two separate ways.

CLI command

Indeed you could open BASH and type a command to get the color selection tool with zenity (works in Wayland and X11 and, on Ubuntu 22.04, requires no additional libraries):

zenity --color-selection

you can even automatically copy the output (which is an RGB color) with the following command, that can be conveniently set as an alias:

zenity --color-selection | xsel --clipboard

But if you, like me, find this a bit painful, read on.

Keyboard shortcut + HEX output

If you want to take stuff to the next level, you can set the above command to be called via keyboard shortcut. To do that:

• re-write the above command as a function
• bonus: append some functionality to convert the RGB output to HEX (which is what I need for instance in React Native and could be useful to others as well)
  • e.g. convert rgb(255,255,255) to #ffffff
• encapsulate it into a my_function_script.sh file

#!/bin/bash

function pick-hex() {
  # Pick a color and return it into the clipboard as HEX, not RGB

  # Use Zenity to select an RGB color
  color=$(zenity --color-selection)

  # Remove the "rgb(" prefix and ")" suffix
  color=${color#rgb(}
  color=${color%)}

  # Split the color into individual RGB values
  IFS=',' read -r red green blue <<< "$color"

  # Trim leading spaces
  red=$(echo "$red" | xargs)
  green=$(echo "$green" | xargs)
  blue=$(echo "$blue" | xargs)

  # Convert RGB to hexadecimal
  red_hex=$(printf "%02X" "$red")
  green_hex=$(printf "%02X" "$green")
  blue_hex=$(printf "%02X" "$blue")

  # Combine the RGB values to form the hexadecimal color
  hex_color="#$red_hex$green_hex$blue_hex"

  # Copy the color to the clipboard for use in other applications
  echo -n "$hex_color" | xsel --clipboard
}

pick-hex

Once the above is in place, setup a keyboard shortcut for this script in Ubuntu:

• go to"Keyboard Shortcuts"
• add a new custom shortcut and click the "+" or "Add" button.
• in the command field, enter the path to your script (e.g. /path/to/my_function_script.sh).
• assign a custom key combination to the shortcut e.g. I like shiftaltc

and you end up with a legit color picking tool called via keyboard from anywhere in Ubuntu.