The original sculpts for the Necron models hearken all the way back to the Space Crusade days (the design being a 'chaos android' at the time). The next incarnation of the Necrons was in metal and rather disappointing, and honestly I was never really thrilled with many of the current-era metal models either (the Immortals and Flayed Ones were a PITA to assemble, and the tomb spyder left me cold). I have high hopes about the next wave based on the frankly excellent plastics GW has been releasing these days. As I was pressed for time (aka painting them the morning of the game), these Necrons were given the bog-standard metal-and-green scheme. If I attempt to do a Necron army nowadays, I think I'd try a sandstone and blue scheme instead.
Alas, this Necron Lord and his small force of Warriors and Scarabs has sat idle in the figure cabinet since that day. There may come a time when the Servants of the Star Gods will not be so quiescent...