YIKES, UGLY YELLOWING OF HEALTHY IN BLOOM PHALS??

[Jkelee]

Help me Puh-weeeze!!

I have a few phals in bloom/bud/spike that have been progressively turning yellow on thier UPPER leaves?!? All in just the last week. And nothing has changed in my habits. There must be about 40-50 more phals hanging out in my chid hotel, but only these in the pics are doing this.

Is this normal for Winter time? Normal for the TOP leaves to do this? And Even in Bloom/Bud/Spike?
As all bud 1 of them are.

They've all been soooo happy and healthy mounted hanging in their home for at least 6 months now. With the same habits from me.
The only thing that changed, was the weather, last week. Some cooler nights. BUT, why aren't ALL my phals doing this yellowing, IF it was the cold?

I'm sorry, but I'm just sick over this
My babies have been sooo very happy out there in their new home, that I don't know what is going on??

Plz help US

The flowers pic is of these phals.