What objective arguments can be provided to prove that a colour scheme for an app is bad?

We have a design for an app developed by an external agency and our business people seem to be happy with it. But it’s really terrible - the colours are too bright, the text is difficult to read and so on.

How can we persuade our business that it needs to be changed? We can’t just say “We don’t like it, it sucks.” We need to have valid points against this colour scheme.

I understand that colours are subjective. But are there any objective metrics that can show the difference between bad and good app colour scheme?