What this means is one or both of your birds is split to another color mutation. This is when they carry genetics for another mutation without showing any visual markings of that mutation. It is quite a surprise for the owner, but not rare. There are so many cockatiel mutations now, most are likely split to another mutation. Congratulations on your surprise colors!
I do want to ask, when you say “lots of clutches”, are you resting your pair in between each clutch? It is very important to remove the nest box after each clutch and rest the parents for 6 months. You should limit them to two clutches per year. In the wild, they actually only produce one per year. Then there are seasonal changes and they do not breed again until the next year. Since we provide the ideal breeding environment for cockatiels year round, we need to make them rest between clutches. It’s very hard on the hen each time she lays eggs, and she needs the rest in order to rebuild her resources.
Thank you for asking Lafeber,