I know that mutations could lead to a "new" plant - I would be happy if this was one of the existing and known ones, that I don't have...

Rina,

I'm sorry to disappoint you. According to my observations, green cells grow faster than white ones on Tricolor. And, if your plant began to lose its variegation due to excess nitrogen, then nothing will save it.

Oksana

Thank you for your comments.

I do not think my succulents will have excess N - I hardly ever fertilize them, they get some fert solution in summer, perhaps 1-3x. The all are grown in very inorganic mix (grit+perlite, with maybe 10-15% of turface or soil or cocopeat added) With probably close to 100 plants I grew over past 8 years - most eventually given away - (all from the original plant), I do not remember similar colors. But I didn't really think it was 'special'.

Would you recommend cutting off that branch a potting it separately?

Rina

Perhaps this plant had received enough nitrogen to grow completely green leaves. An usual green obliqua will grow from this branch.