jeffersondem: "When you get a better engine, search Benjamin Burton, Republican, Delaware. Slaveowner."
In 1860 Delaware had fewer slaves per capita than any other slave state, and Burton with 28 was said to be the state's largest slaveholder.
In 1862 he met with Lincoln to negotiate compensated gradual emancipation, similar to but more generous than abolition in Washington, DC.
Lincoln had great hopes for the abolition plan he negotiated with Burton, it could set the example for other Border slave-states.
But Burton's plan was defeated in Delaware's legislature, twice, both times by one vote.
So, yes, Burton was a slaveholder himself, but also active in the abolition movement.
As for which party did 1860 secessionists belong to, Green are Breckenridge Democrats, Brown are John Bell's Constitutional Unionists.
Democrats were, of course, the party of slavery, while Constitutional Unionists were strongest in areas with fewer slaves or stronger commercial ties to the North.
As their party name suggests, Constitutional Unionists opposed secession in early 1861. 