Golden Plants

[Zillah]

Does anyone know what makes plants go gold?  I have a Fatsia which was green
when small, but is now very golden-green -  and makes a very bright accent
in the garden.  I know there are many other golden cultivars of other plants
such as Pelargoniums (e.g. Mrs. Quilter) and the Choisya called I think
Sundance.  Just wondered how they come about initially.
Thanks for reading this -