Quackers discolours easily, so a nice white one will always gain attention (although tbh I think it's a risk buying one, given that probably it will be snared by the age demon sooner or later).
With Windy, there are various batches with different density of purple, and some of them end up paler than others. There is no 'white windy' per se, but Windy can exist in different shades and some were never as lavender as others. That doesn't make them more expensive or rare though. I would think a nice lavender one would probably fetch the best price, as that's the way Windy ought to look.