I saw the screenshot and thought: Wow! That's nice idea to randomize background color. It will definitely look less boring when you have four or more terminal windows. Though I wondered why there is no indication of randomization in the pasted code. I just assumed it must be somewhere.
I quickly wrote a couple alias for randomization of background color when I had time:
alias urxvtrb='urxvt -bg "#$(echo $RANDOM | md5sum | head -c6)"'
# If you like gray scale
alias urxvtrb='_C=" " ; urxvt -bg "#${_C// /$(( RANDOM % 6 ))}"'
This can be developed into a full set of color randomization for all 16 colors. It will be very awesome and fun. Just need a good algorithm or may be presets of colors. Terminal can be much more fantastically colorful than you can even imagine.
But hours later, before I write this post, I checked up the thread again and saw this reply. LMAO.