Rant: Client's color choices made my chart unreadable for my colorblind brother

I designed a data chart using a client's strict blue and purple color scheme. My brother, who is colorblind, told me the sections all looked the same to him. The client says changing colors would hurt their brand image, but I think it's wrong to ignore accessibility. Now I'm not sure if I should push back or just do what they ask. What's your take on balancing brand rules with making designs work for everyone?