Here are some park data for the Eastern Colored League, 1924. It’s only one season, so isn’t close to the final word about these parks, but every little bit helps. The numbers are: park factor for runs (or simple home/road ratio; that is, runs scored in home games divided by runs scored in road games, multiplied by 100), adjusted park factor (same thing, adjusted for proportion of home to road games); then in parentheses the number of home and road games. Harrisburg and Atlantic City have not been completely researched yet (games come from the Pittsburgh Courier).
Bacharach Giants, Bacharach Park (a.k.a. Inlet Park, Atlantic City): 107, 104 (26, 20)
Baltimore Black Sox, Maryland Park: 81, 87 (37, 18)
Brooklyn Royal Giants, Dexter Park: 136, 102 (2, 32)
Harrisburg Giants, Island Park: 92, 97 (15, 22)
Hilldale Club, Hilldale Park (Darby PA): 82, 88 (40, 19)
Lincoln Giants, Catholic Protectory Oval (Bronx): 129, 121 (41, 16)
Washington/Wilmington Potomacs: 113, 106 (26, 27)—OVERALL
Griffith Stadium (Washington DC): 128 (14 games)
Wilmington DE: 95 (12 games)
Other than the Lincolns’ Catholic Protectory Oval, which was a very good hitters’ park, possibly on the level of Stars’ Park in St. Louis, I don’t have a very strong sense of the ECL parks yet. The Royal Giants’ Dexter Park is just here to complete the list, as I’ve so far found only two games played there (it can hardly be said to have been their home park). The Cuban Stars were evidently a traveling team this season. I don’t offhand remember the name of the Wilmington park, though I should know it.
UPDATE 4/19/07 I should have pointed out that I also have park factors for the Negro National League, 1920-24, posted here. They will be updated with fresher research soon.