Don,

Congratulations, that's a very variegated sport you have found.

Follow Tim's advice, cut it of the mother plant, and give it a special place in the garden.

I have a Yucca 'Golden Sword' which has gone back to normal green form, not as interesting as yours, when it's the other way around. But when it bloom one day it can produce seeds which have clorophyl.

Have a nice day

Benny