Color rings on a wall

How to choose colors effectively

Here is a simple, scientific rule that can make your colors much nicer.
UI of gradient mesher app

Mesher by CSS hero

Here is another gradient generator. This one also comes with a WordPress plugin.
Glass on the rgb colors

HEX to RGB converter

Add your hex code in the form and the tool will generate the RGB values.
Color palette

Color shade generator

Add your default hex value, and this tool will generate all of the shades.