Q.Why did my Crown of Thorns plant (potted) leaves turn white when I placed it outside?
This potted plant is several years old and was given to me in March 2019. I kept it indoors and it adjusted well. I placed it outside May 21 and the next morning the leaves had started to go white. Too cold? I have now brought it back in until I can find an answer.
If temperatures dropped too low; it certainly could be frost or cold damage.
Also when moving plants from indoors to outdoors you need to harden them off; gradually adjust them to the light change.
Give them a sheltered area to make the adjustment to outdoors; gradually increase it to a full sun location.
These articles will help you.