*rubs skeleton units*
You have got a good transition on the white side of the minis. It's not always easy to get that effect.
Maybe, I do not know for sure, you should use swampy or Sylvanian muddy ground (think cart tracks.) From what it ooks it's all stone! A bit difficult to crawl out of. Anyway if you saw and played Ultima 8 that's ok. In there, there are stony graves, crypt & mausoleum style. Elsewise good basing but needs woods, leaves for example. Did you want to put the bases inside a prepared GW movement tray ?
Your wood on shields looks damp (see swampy above) which is good.
Anyway try to steer clear of simple color schemes and contrast rust and wood for undead together with some greens.
MS.
PS:
If you do not find enough about undead try to find the skeleton painting article of WHFB rulebook or bestiary, I don't remember, 4th edition, sharing sites could offer it. There's things in there like orange wash on bestial brown for rust. Your rust effects seem to be missing.