Yes, thanks. Venera is a lutino budgie and Apollo is a cobalt blue budgie with (I think) yellow face type 2 factor. Both have mutations, both always argue...

The reason why you cannot have white face green budgies is because green budgies are yellow based and their genes are dominant. A blue budgie is white based recessive and their genes remove yellow pigmentation. A white face green budgie is not possible because in order for white base, you will have to remove yellow pigmentation and that lack of yellow makes blue feathers. Green needs yellow.
But yes, yellow face blue budgies are possible...