Whenever I used a dark colour scheme for vim (like the excellent muon or getafe, I find myself lost beacuse the usually black cursor of my urxvt wouldnt adjust to the dark colour theme. I found that this cant be tweaked in vim, but one can change the color of the urxvt terminal; so, for my needs, putting the following into $HOME/.Xresources:

URxvt*cursorColor:  #D6C0FB
URxvt*cursorBlink:  on

does the job pretty satisfyingly :-)
(for reloading the Xresources, use xrdb -load .Xresources. put the same command into ~/.xinitrc to have it loaded on X startup)