Anyone who has been designing for the web for more than a year or so ago is likely to have heard of the browser-safe palette, a set of 216 colours recommended for use on the web as they represented the intersection between the 256 colours supported by both Windows and Mac computers in the late 90s. Few computers these days are limited to 256 colours and the browser-safe palette has been consigned to history.
The concept of a smart palette for the web has not died completely, however. The Web-Smart palette, a colour-cube of 4,096 colours that should display consistently on displays that use both 16-bit (thousands of colours) and 24-bit (millions of colours). The linked site includes a dynamic colour cube and slider for exploring the web-smart set of colours.