Subtle has no negative connotation. It just means not very obvious. Any negative or positive connotation in the sentence would come from whatever is described as subtle. There was a subtle smell of lavender - positive. The waiter was subtly rude - negative.

Hi Rachel, subtle is neutral. In this case, it could be negative or positive, depending on the context. You can change your language level under settings, btw. Let me know if you need help with that. Anyway, I can help you improve your English. I also know Chinese. Please check out my profile and feel free to book a lesson :)

For my part, it isn’t so negative which just means not very noticeable or obvious.