Hi Naoki and Bud,
On the alba form the entire flower is white and on Naoki's flower, the base of the lip still has a blue spot. Then with the alba form, it is the whole spike who produces white flowers, not a single alba flower among other blue ones.
Some photos of the alba form ( who was in fact registred as Vanda coerulea luwangalba in 2008) that I took during a show in Bangkok :
Vanda coerulea alba | Flickr - Photo Sharing!
But I used to have the same experience than Naoki next to pollination of V. coerulea with a flower who became white.
All my best !