W3Schools.com is full of useful resources, including:
Browser Statistics – Featuring W3Schools' Famous Month-by-Month Browser Statistics Since 2002 Also includes the most popular operating system platforms, screen resolutions, mobile devices, plus break-outs for Chrome, Firefox, Internet Explorer, Safari, and Opera browsers.
HTML Color Picker – Pick a color or enter a code to see the color. Also includes many other color related tutorials. Many have associated tools.
Color Converter – Enter a color or code to translate it into other schemes. Includes: color name, hex, rgb, hsl, hwb, cmyk & ncol schemes.