Cinta,
As far as I know. It can't be done. Sorry. New growth could come in darker or lighter. I heard it depends on how much light it gets. More light, lighter color. There are some others like 'Siam Silver', or maybe 'White Striped Giant'. but not sure it they also darken with age and will throw the whole pot off. Some 'White Striped' is actually Bantel misnamed.
