My plum headed parakeet's upper beak has a black patch

[Lijoks]

In all the images i have seen the upper beak is supposed to be yellow and the lower one black but in my parrot the upper beak has black patch (as big as the lower beak) and the lower beak is yellow. He/she is about 6-7 months of age. Is it normal??

 

[Zoruace]

In all the images i have seen the upper beak is supposed to be yellow and the lower one black but in my parrot the upper beak has black patch (as big as the lower beak) and the lower beak is yellow. He/she is about 6-7 months of age. Is it normal??

Best take him to a vet for check up if he is fine then its normal-ish?