The next halo ring or circle will take the inner color of the selected ball. So you can plan ahead a bit.
There are also wildcard balls, which will match any color. Use them when needed when game gets faster.
Occasionally bombs apper that will take away some balls, so be quick to use any good balls before they are gone.
Game has global high score table, so you can see how well you are doing compare to other halo players in the world!