As I go around peoples gardens variegated plants are common. Variegated Euonymous, Pittosporum, Ivy, plus lots of less common plants.
Not all, but, most of them will revert to solid colored foliage. Some varieties more than others but most of them will revert. The plants that are sports tend to be the worst. Sports are branches that spontaneous changed to a variegated leaf. Because genetically the change is only skin deep they can change back.
As you look at variegated plants you often see branches that have reverted to solid green and others that have continued the change to solid white or yellow. The branches that have reverted green tend to overtake the entire plant. If you think about it the reason is obvious. Green means chlorophyll. yellow or white means little to no chlorophyll. The branches with lots of chlorophyll have more energy and grow more vigorously.
If you have variegated plants that have green branches mixed in with the variegated branches you need to cut ALL the green branches back to where all the branches left go to variegated foliage. You need to be ruthless about this. If some of the branches are all yellow or white you can cut those back also, but because of their lack of chlorophyll they don't tend to take over.
At my yard I recently planted a deep purple coleus with a green and yellow green variegated coleus. After pruning the green coleus back twice, the green one is still twice the size of the purple one. The purple one looks great. Its just that it is much slower growing.
More chlorophyll means more growth. Off topic, this is why when you prune plants TOO hard when they are young they can just quit growing and sulk until they have had a chance to replace the pruned foliage.