How to change comments font colour?

I’m using the Sliding-Door theme for my site and I’m having a bit of a problem. I’m using the dark-theme colour and all comments fonts are white which should be fine except that the comment bubble is also white. It worked fine if I switch to Light-theme as the font will be switched to black.

The way I see it, it’s either I find a way to change the font colour or change the bubble colour. Any help here is greatly appreciated.

Thanks