From Kraytracing Wiki

Background

background color,color

Sets background color to grey.

Example: background color,(0.5,0.5,0.5);

background sky2,ground color,sky color,nadir color,zenith color,zenith direction vector

Example: background sky2,(50/255,40/255,30/255),(120/255,180/255,240/255),(100/255,80/255,60/255),(0/255,40/255,80/255),(0,1,0);