color: hsl(<hue>,<saturation>,<lightness>)

Supported by Opera, Firefox, Chrome, Safari and not IE7

hue

0 (red), 120(green), 240 (blue), 360 (red)

saturation

0 to 100% (full saturation)

lightness

0 (black) to 100% (white)

<p>
<span style="color:hsl(0,100%,50%)"> Red </span>
<span style="color:hsl(120,50%,50%)"> Pastel Green </span>
<span style="color:hsl(240,100%,75%)"> Pale Blue </span>
<span style="color:hsl(240,100%,25%)"> Dark Blue </span>
</p>

Red Pastel Green Pale Blue Dark Blue