[WP Touch] : how to Change color of the Comment Bubble on the front page?

I found that whenever there are some people leave a comment in a post. There will be a small bubble “in red color” appear on the front page, reminding me how many comments left on a particular post.

I would like to know how to change the color of that bubble ? I thought it’s related to the /core-images/sprite.png, but I’ve changed its color and even deleted it, nothing happened ?