0to255 is described as 'simple tool that helps web designers find variations of any color. Perfect for hovers, borders, gradients, and more' and is an website in the Photos & Graphics category. There are three alternatives to 0to255, not only websites but also apps for Windows,.NET Framework, Android and iPhone. The best alternative is ColorManager, which is free. Other great sites and apps similar to 0to255 are Colorizer.me (Free) and Image Colorizer (Free).
Color Manager is a color management utility. Color Manager expects colors in RGB, CMYK, HSV, YUV and hex value to for all sorts of purposes (for example, colors of an application or website). In the pipette mode can also easily one color can be chosen from the active desktop.