Paul,

With recent software updates Ancestry.com now has two (2) search capabilities.
1. Old Search
2. New Search

Below using the Old Search is an example of the 1850 Census search screen indicating "color" as one of the search parameters.

I called Ancestry this morning and the 'person of color' feature on the African American Historical Record Collection for Census records is inoperable at this time. The Tech Support people have been made aware of the problem and are going to be working on resolving the problem.

Searching (old search) the 1850 Census for Thurston's of color I used: exact matches only, the wild card feature of thu* as the last name, all states and color=black. There were 53 hits, those that appeared as Thurston were:
1. Maria Thurstin Towanda, Bradford Co.,PA bca 1815 in PA.
2. There were 19 Thurston and they were found in TN, RI, NY, DC, Conn & Mass .... none in VA.

Hope this helps,

Art Thomas