Hi, the game works great. I like the strategy element, its not apparent at first play but you have to keep an eye on the color of the border changing as the bad color bubbles you let go by before the color changed will hit the top and cause point loss.
I think that if you wanted to keep the game idea going and add more to it in terms of content. Break the gameplay up into rounds, perhaps a bonus round for reaching X points, and finally some type of timeout after the color changes so that bubbles a few pixels away from the edge before the color changes don't take away hearts.