Changing site title color on mobile page

I am using the Retina theme, which does not have a mobile version, so I have the jetpack mobile version activated. On Retina my header text is white, which means the jetpack mobile page has my site title in white on a white background. I just want to change my site title to another color for the mobile version only.

Going into the Edit CSS page I have the Mobile Compatible option set to yes and I am using the .mobile-theme command, but I cannot figure out how to get the code to work. I have virtually no CSS experience (so sorry if lingo errors) but feel this should be simple, I just can’t find the command to use. Please help! Thank you!