Purple:

Left - A

Right - D

Jump - W

Spit - S

Green:

Left - left arrow

Right - right arrow

Jump - up arrow

Spit - down arrow

You can only get 1 point per platform (even if you have multiple balls on that platform of your color, it still only counts as 1 point). Spitting at the other color ball will destroy it. Spitting at the other player will push them back.