Many websites have the ability to 'shop by' all sorts of different methods...

Shop by price
Shop by department or category
Shop by brand
Shop by gender

Buckle, a multi-channel retailer specializing in casual apparel, footwear, and accessories, has the ability to 'shop by color'. Taking it to the next level, they had a fantastic email last week touting their 'green' product line with the ever desirable pitch to be "Irish for a Day".

I love the fact that the sales links take you directly to the 'green' products.

A nice, clever way of sprucing up a standard promotion and leveraging the fact that St. Patrick's Day is only a week away.

An example of the creative is below: