What's a fabric key? It's a tool to help you sort out and keep track of which fabric to use where in a quilt design. It's especially useful when you plan to use different fabrics than the pattern cover quilt.
For the the last several years I have included a fabric key in most of my patterns. Here's what the fabric key from Shiny Blossoms looks like. It's sharper in the pattern. Saving parts of the pattern as pictures to insert here made them fuzzy, but you get the idea.
Match up the fill of a component of the design in the diagram with the matching fill in the table to identify how the fabric for that component is named in the pattern.
You can use the key in two ways. First, it can help identify how the fabrics in the cover quilt are labelled in the pattern. Comparing the pattern fills in the diagram and the table, I see that Fabric 1 is used in the center star. Comparing the photo to the diagram, I can figure out that the star is made with Fabric 1.
Knowing that, I can refer to the fabric requirements for the right amount of fabric for the various components of the quilt.The second, possibly more important use of the fabric key is to keep track of my fabric choices as I work through the pattern making the quilt.
In the example above, I planned to use the floral in the star, and working back through the diagram I knew to use that wherever the pattern references Fabric1, or where the diagrams use the pattern fill for Fabric 1.
I recommend jotting down description of the actual fabric you've chosen for each fabric. You can use the fabric name, or its color, or describe the print. You could take it a step further and make things even clearer by snipping a small swatch of the fabric you chose and taping it to the table beside the appropriate label.