The plus point to growing an evergreen variegated shrub is the leaf colour which the variegation brings, especially in the winter. It can happen though that over time the shrub starts to throw out stems which are plain, they have lost their variations. In the images below, on the left is a popular, evergreen garden shrub Elaeagnus Pungens 'Maculata' a bit of a mouthful, but looking the images shows it's bold, brightly coloured variegated leaves. It's a great garden shrub as it is fast growing which makes it good for hedging, suitable for coastal gardens, tough and tolerant of many conditions.
In common with other variegated shrubs it can start to grow shoots without variegation, as in the image on the right. This is called 'reversion' and maybe caused by low light levels especially as variegated shrubs are often grown in semi shade and they may have a lower level of chlorophyll. Winter is a good time to check shrubs, and if you find some shoots with plain non variegated leaves, the solution is to prune them out to maintain the variegated nature of the shrub. This will not do the shrub any harm and keep its interesting colour. Just cut off the non variegated branch close to the trunk in a clean cut, and prune out all other non variegated shoots. This is best done during a mild spell or left to early spring.
More about Growing Evergreen Shrubs