Adobe Color
A very useful free color wheel and color palette generator for designers and developers. You can also upload an image to get colors from it.
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ColorSpace
Color palettes generator, ColorSpace is a space for everything that has to do with color palettes and gradients.
ColorHunt
Color Hunt is a free and open platform for color inspiration with thousands of trendy hand-picked color palettes.
Grabient
A great tool that generates linear gradients, with the ability to customize each gradient, and download the CSS gradient code.
Gradient by ShopFactory
Gradient by ShopFactory is a great tool for finding wonderful gradients, to use in your next project. It allows you to control the gradients based on different settings.