I have white and green. Its ugly. And I had natural with blue and red also ugly. But I took the natural and blue and red out and still waiting to replace the white and green.
I used black and white, it worked well with convicts - but didn't do much for african cichlids when I tried that. I switched their tank to all black, colors pop more now.
In my old sw tank I tried red white and red, trying tomimic a canadian flag lol after about two mo ths it all blended together to a pinkish colour. Still looked cool though.
I have used a natural fine gravel mix - mainly whites, greys, and light browns - and then mixed in chunky rose, orange and rust colors rocks for some accents. I have been really happy with it because they are all natural rocks.