why has my euphorbia variegate starting growing plain green leaves

[Calley]

[rowanwitch]

Reversion is common with variegated shrubs cut out all the plain green growth or it will start to take over as the plain green is more vigorous

Once a shrub starts this you need to keep an eye on it as it will keep on producing green shoots

[AlBags]

I agree .. It's trying to revert.
Cannot be cured.

[muff13]

It is important that you cut off any green shoots as they are stronger growing. Just keep an eye on the bush and remove any green shoots when they appear and all should be well.