I agree with everyone about the color change being from temp. change. I have two posts on here of one of my plants called Slc. Beaufort. When it's colder there is less color on the lip. But I've also heard with some whites, if you use different or less fertilizer it affects the amount of yellow in the lip. A white like Wedding Song.... IMHO it is the temps....but then I'm still relatively a baby at this.
Connie