Like real-life billiard balls, 9-Ball is yellow, just like how 8-Ball is black. However, real-life 9-balls are striped, not solid. This pattern belongs to the 1-ball. A real 9-Ball has a yellow stripe in the middle with white on the top and bottom.
Tune later appeared in BFDIA 5b as a NPC, 9-Ball later appeared as a recommended character that could join TPOT, and A duck later appeared as a contestant in BFDI Mini.