One of the main reasons most of us Rom or have Rommed our phones in the past is for the Rom themes. These themes are even more in depth than those themes you can get from Samsung or HTC's theme stores. CyanogenMod theme engine themes and Layers themes actually theme every part of the Rom including apps.
Google apps are not generally theme ready. Items like text and background colors are hard coded in layout xmis. This makes these particular apps very had to edit. DJDarknight and TeamBlackout have released versions of the Google Apps that are theme ready and compatible with Cyanogenmod Theme Engine and Layers Themes.
Head to the link below for more information and download links.
via XDA