I'm not. I really fail to see where do you see frontend development to be easier for AI to pick up compared to backend. As I said frontend is writing code for an user interface and backend for a machine interface.
Knowing that a white font is not visible on white background is not really a design job is it? Calling an API on the other hand requires mostly logic and documentation or do you disagree?
Forget AI exists for a moment. You’ve got a team of humans working on a project. You’ve got a backend developer, a frontend developer, a DBA, a platform engineer, a graphic designer, a UX person, a product manager, and a QA person.
Whose responsibility is it to select the colours? You think this is the responsibility of one of the developers‽ You don’t think “having taste in colours” is solidly owned by the designer‽ You think this is a developer task not a design task‽
Aside from that, the specific example you chose is an area where we have deterministic algorithms for judging contrast – we don’t even need AI for that, regular old procedural code can do it.