Truthfully I feel they're at least Violet, he was training with Chen Fei in the earlier chapter meaning his talent has to be on par at the very minimum. The fact that Chen Fei is already a cultivator though and But Cai caught up and even surpassed him leads me to believe they're Gold or Black, even further evidenced by the fact that Chen Guanting said that he was their only 16yo Qi Condensation cultivator.