I agree with Pat. 

I'm a product of several generations described as mulatto [with no immediate
traceable white ancestor].
On just one line of my family, my maternal great grandfather and siblings were
all described as mulatto. And their parents, grandparents and
great-grandparents were all described as mulattoes.  

My great-grandfather was a lighter-skinned man. His siblings were darker
skinned with soft and straighter jet-black hair.

I think the census taker wrote down whatever they thought they saw, or what
they were told.

At one point, a line of family in Jamestown, Ohio described themselves in a
very confusing way.
Three brothers, all who shared the same mother and father, were described as
mulatto, Indian and white.
One brother was marked as mulatto. Right next door to him, his brother was
marked as Indian. A street away, the third brother was marked as white. Ten
years later, the white brother was marked as mulatto, and the Indian brother
was marked as mulatto. And the mulatto brother was marked as Indian.

It really depended on what the census thought he saw, or what he was told
[whether it was the truth or not; whether it was what the people themselves
were told about themselves or not].

Keith Josef Adkins
Ayers-Lynem family historian
playwright/screenwriter