Welcome to the forums! 
There can be a few reasons for the cere of a male budgie to turn brownish in colour. Besides the colour change on the cere, I also notice your male has dark stains on the feathers above the cere.
What is your budgie's diet? Does he have a varied and balanced diet?
It's possible that he has a vitamin deficiency problem.
Another possibility that would explain the colour change on the cere would be a hormonal imbalance or God forbid, cancer on the reproductive organs.
Your budgie needs to be seen by a specialized avian vet so that he is properly checked, diagnosed and treated.
I'm sending my best wishes and hope your budgie's condition improves soon.
There can be a few reasons for the cere of a male budgie to turn brownish in colour. Besides the colour change on the cere, I also notice your male has dark stains on the feathers above the cere.
What is your budgie's diet? Does he have a varied and balanced diet?
It's possible that he has a vitamin deficiency problem.
Another possibility that would explain the colour change on the cere would be a hormonal imbalance or God forbid, cancer on the reproductive organs.
Your budgie needs to be seen by a specialized avian vet so that he is properly checked, diagnosed and treated.
I'm sending my best wishes and hope your budgie's condition improves soon.