title: Magento product list page - group products by color attribute
body: <p>I need a help with magento. There are two attributes for creating configurable products, size and color. On the category page where products are listed, I want to display only different colors of products not sizes. I've to group products by color.</p>
  
  <p>I.e. if there is a shirt with colors red, blue, gray, black and for each color there are a sizes M, L, XL (there are 12 simple products), I need to display only 4 products grouped by color.</p>
  
  <p>Thanks in advance</p>