>>95938100
The opposite of icy blue is a coppery-orange color. It also by a nice coincidence, means that verdigris looks really good on copper
now granted despite being all metallic I've never seen anyone do rust or verdigris on necrons, dunno if there's a lore reason for that, but you could make their metallic skeleton be copper (game's workshop's Brass Scorpion is a very bright copper) and then use ice-blue for their glowing eyes and glowing weapons. Maybe even ice-blue shoulderpads if you're one of the people that do non-metallic necron shoulder pads.

The other two colors, the purple and pastel yellow, are just 90-degrees on the color wheel from ice-blue/copper, use them if you want to or don't, up to you