I want to first began by saying brown-skinned people always considered themselves on the dark-skinned side, when it came to light skin and dark skin.
A lot may not agree, but I think people who come from a predominately Black environment have pretty much the same perception of who they'd consider dark-skinned and who they'd consider light-skinned, and who they'd consider is some where in-between. Even though there's a larger grey area than it was when I was coming up, and it may not be as easy to agree on someones skintone as it use to be (probably because of more mixing), I still believing as a group, we have pretty close opinions on skintone for the most part. For example in my predominately Black high school, we all agreed on who was in the light-skinned category, and who was in the dark-skinned category, while few were labeled some where in-between. If I saw these same classmates today, we'd still have the same opinion. But I will admit, when viewing my high school yearbook, some of the students I considered in the light-skinned category, including myself, don't look quite as light as they did back then. But they still fall no where near the dark-skinned category, or even the brown-skinned category.
I believe most of the confusion come from people giving their opinions on the internet, but aren't even Black.