This is a great little web app.
A color wheel that, as you mouse over it displays the hexadecimal code for the color, it's closest websafe corollary, and the closest websmart color, as well as showing you those colors. That in and of itself makes it a powerful visualization tool and resource.
But if you click on a spot on the wheel, you not only get the above codes, you get a a value scale of the color, and the color gets saved in a sidebar with the websafe and websmart codes. Click on more colors and they stack in that sidebar, so you can build a color scheme.
Once, long ago, monitors could display only a restricted number of colors without dithering or other color discrepancies. The traditional solution to this problem was to use a restricted color palette known as the Netscape 216 colors, browser-safe colors or the web-safe colors. In hexadecimal form, the web-safe colors are composed of three pairs of identical hexadecimal digits selected from 00, 33, 66, 99, cc, and ff; for example, #000000 is black, and #cc0000 is red.
Time passed, as it so frequently does, and new hardware supported thousands or millions of colors. People grew tired of the old 216 colors. They wanted more earth tones, more variety. The web-smart colors are those 4096 colors composed of any three pairs of identical hexadeximal digits (0-9 and a-f), such as #dd1188.
The unsafe colors are the full set of 16,777,216 hexadecimal colors, featuring any color between #000000 and #ffffff, such as #5a832d.