Lycaste skinneri alba.
This is the real 'Monca Blanca'. A previous post showed an almost real one, the yellow throat is one of the give a ways. It made it's first bloom just before Xmas and has produced flower after flower since then. I gave it to my Guatemalan in laws to include in their Xmas celebration and have not seen it since. They worship that thing and won't let go of it until it finishes blooming.
Finally got a picture of it which I did not take. It is white all right but I suspect the whiteness has been enhanced a little.