I am a statistics geek, and I did something similar on a blog that I write. I used
J.D.B. Debow's "Statistical View of the United States, Compendium of the Seventh Census," published in 1854. (http://www.archive.org/details/statisticalviewo00unitrich)

I compared the years 1790, 1820 and 1850 and found that the percentage of the population listed as "free colored" was consistent at 2%. Interestingly enough, the slave population percentage of the total population decreased in that same period from 18% in 1790 to 16% in 1820 and 14% in 1850.

I was also curious as to which states had the largest percentage of free colored living in the state. Delaware was the hands down winner in all three census years with 6.6% in 1790, 17.81% in 1820 and 19.75% in 1850. (Louisiana, by contrast came in fourth in 1820 with 7.15% of total population and sixth in 1850 with 3.37%.)

The compendium also gave the top occupations for free colored persons in the 1850 Census living in Connecticut and Louisiana. The top six for Connecticut were Laborer, Mariner, Farmer, Servant, Shoemaker and Barber. In Louisana the top occupations for free colored were Carpenter, Laborer, Mason, Planter, Cigar Maker and Farmer.

If anyone is interested in reading the full text of my post along with seeing every statistic geeks favorite tool, the pie chart, you can reach it at the link given below.

(FYI My free colored line comes from Virginia.)