This is observed in the 6u10 b07 pit build on all OS with Nimbus L&F. 
Black color appearing as white in a ComboBox inside a JTable.
Run SwingSet2 and tab to the Table demo. Drop down the Combobox in the "Favourite Color" Column and select Black. 
Expected Behavior: The Cell is rendered in Black color.
Actual Behavior: The Cell is rendered in White color.
Attached Image for reference.
Black color is appearing as grey in a ComboBox inside a JTable in 6u10b09 pit build.
Run SwingSet2 and tab to the Table demo. Drop down the Combobox in the "Favourite Color" Column and select Black. 
Expected Behavior: The Cell is rendered in Black color.
Actual Behavior: The Cell is rendered in grey color.