Kitty, as for the zygo in the library and red hue, it's most likely sunlight..Somce may consider it sunburn..still, it's common w/zygos, especially once strong summer light hits leaves.

Wilting is caused from too much or too little water..When you set outside, did you do so gradually? In other words, did you first set in a shady spot, then set in a brighter area?
Zygos need to be watered well, then soil should dry a bit between waterings. Not constantly wet or dry.
When a leaf is on its way out, it turns yellow..
Was your plant ever fertilized? Toni

Thanks for responding,

Since I got it from an evil box store 3 or 4 ago months the cactus has been sitting on a covered porch where it usually gets plenty of indirect light. The temperatures have been up around 90º thisz past couple of weeks tho'. I water it once a week, using rainwater from a kiddie pool under the eaves that my 2 ducks play in (um...the water is a bit...'enriched'...by the girls). Every couple three weeks I also add a capful of ammonia per gallon and a dash of instant tea, per a Jerry Baker book.

Hmmmm, would be that be it--overfertilization? A Thanksgiving cactus wouldn't need the extra 'enrichment' that the foliage plants would like.

Any suggestions on how to best help the plant recover?

Thanks,

Kelly