ColorWell - Your Privacy is your business
Just Color Picker - Free portable colour picker and colour editor for web designers, photographers, graphic designers and digital artists. Supports Windows and macOS.
KColorChooser - KColorChooser is a simple application to select the color from the screen or from a pallete.
Instant Eyedropper - Identifying the color code of an object on the screen is usually an involved, multistep process:...
Sip - A better way to collect, organize & share your colors.
gcolor2 - GTK+2 Color Selector