Photoflare
Photoflare – free and open source, fast and simple, but powerful cross-platform image editor
LazPaint
LazPaint – free and open source, cross-platform light editor of images with multiple tools and filters
LightZone
LightZone – free and open source, multiplatform digital darkroom software and professional-level photo editor
Colorpicker
Colorpicker a free and open source cross platform desktop software for determining the color on the screen
ColorPicker App
ColorPicker App – screen color picker application for Linux Desktop
sK1 Color Picker
sK1 Color Picker – advanced color picker application with magnify glass and palette management functionality
Gpick
Gpick is an free and open source advanced color picker and palette editing tool for Linux
Pick
Pick – a software for picking colors on the screen in Linux
Gcolor3
Gcolor3 – free open source software for color choosing (on-screen color detection) and color selection in Linux
Qimgv
Qimgv – free and open source fast, configurable, easy to use image viewer with optional video support for Linux and Windows