I feel like the purpose of the theme is lost now that I can't select a theme at the page level. In Sitefinity 3 I could select a theme per page, which meant that in your example I could have just one template, and have three themes, one for each color. This did not require the user to know css, and it did not clutter my list of templates with silly style specific variations of the same template.
I know this is a feature that has been requested since Sitefinity 4 was released. I understood then that it was completely new code and that there wouldn't be feature parity with version 3 right away, but we're on version 7 now and this feature is still not available. Is this even on the road map?