There are few different approaches to this scenario. It depends how experienced are your content writers, how many colors are you going to support, how many color differences are going to have in the themes. I am attaching a scheme with few different approaches that may point you to the right direction.
the Telerik team
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?
I have a dynamic content widget on a page, It follows theme applied to its template for List view but I want different configurable theme for details view of the content(Maybe configured using a field in dynamic content). Is it possible to apply different themes to a page, details view on runtime?