If you're looking for complimentary colours - then I'll echo Frik_Morkai and say Orange is the way to go - it may even look as if the ice has 'captured' the fire. However, if you want a really overall cold look, then a darker hue of blue would possibly be best.
IMHO, I would avoid green, simply because, for me at least, it suggests neither an overall really 'winter' cold or, as with the orange, the sense that the winter cold is encroaching on heat and forcing it back. Green just seems like a mild spring - neither hot nor cold.
Knives and satchels, or anything leather - I would possibly go with a lighter leather, possibly highlighted with a light blue to give an indication of frost-riming.
As for banners, personally, I wouldn't be too fussed about continuing the Ice theme as the banners will be your spot colour to tie in your army, so I would choose a complimentary colour, maybe not orange, but a red and yellow of some sort.
Of course, these are just my opinions, having never painted eldar the suggestions I've made could be very garish - I just don't know, but it's just a few ideas to help you.