Selecting Colors For the Web

W3Schools' Color Picker allows one to look at a range of colors varying only in one axis of hue, saturation, and lightness; but does not allow one to directly chose values for those three characteristics.

colorpicker.me allows one to change one of the values at a time for four characteristics: hue, saturation, lightness, and value; but doesn't show as good a range of test chips deriving from changing one characteristic at a time.

Also, see the Brewer palette for picking colors for colorblind visitors.