What is the latest version of OS X that I can run on a Black MacBook 4,1 (Early 2008 model?)
As you mentioned, OS X El Capitan will run on the MacBook (13-inch Aluminium, Late 2008) model, known as MacBook 5,1. 

The latest version of OS X that you can get running on a MacBook 4,1 (Early 2008 model) is Mac OS X 10.7.5. El Capitan will not run on the non-Aluminium 2008 models (Early or Late).

I have verified this information against the Mactracker app (not affiliated with Mactracker in any way).