Ever since trader llamas could breed with normal llamas, the babies they produce always end up to be a normal llama, it could end up with either one of its parents colours, but it would not be a trader llama.
Reproduce
Tame a Llama & Trader Llama
Breed the two
Repeat a few times
❌ A baby Llama will be always be born and not a trader llama
Please provide a screenshot of the setup with the F3 debug screen enabled.