This is where you get to pick how -273 looks. -273 will default to shades of grey, but by selecting various hues and saturation levels, you can choose your own color scheme.

Hue is bascially the color of the page. Hues are measured in degrees (think of the color wheel), where 0 is red, 60 is yellow, 120 is green, 180 is cyan, 240 is blue, 300 is violet, and 360 is red again.

Saturation dictates how vivid the color is. Low saturations are very dull, and high saturations are very bright. For example, 0% saturation will give you grey regardless of the hue, while 100% saturation will make the hue you selected appear in it's purest form.

The best way to get a handle on all of this is to try it out. Here a few suggested colors:
    Hue=220, Saturation=30 (steel blue);
    Hue=240, Saturation=20 (ouranophobe purple);
    Hue=40, Saturation=90 (autumn shades).