Rapid pigment change, normal?

So, my husband is really dark-skinned (African American). I have definitely seen him darken in the summer, but he’s also horrific about wearing sunblock. I took our almost three year old swimming today, and made sure she was well-sunblocked with her cousin and I. I am not burned, my niece isn’t burned, and my daughter isn’t ‘burned,’ but does have a dark tan line around where her bathing suit was. We were only at the pool for an hour. My question is, despite being less likely to burn, do people of color take on pigment more quickly in the sun, regardless of SPF? Maybe it’s a dumb question, but I was so shocked to see the distinct line after so short a time, and since I’m very prone to burning, I would think that if it were an issue with the sunblock application either in technique or timing that I would be burned.