Hi, this is my first post and happy to be to "help" here.
What about to go with a theme according the "color/stone" of month? For example...
We all know that green is great for sites related to: health, vitamins, earth, massaging, yoga, etc. Do you imagine all the green tones that can be used for a template? Dark colors even for jewelry and clothing sites... the possibilities are endless.
Hope that helps! :