I've recently started quilting after having sewn for many years.  I often have trouble determining what the undertones to a color are.  Red can have a blue, orange, yellow, etc., undertone and in some projects it really matters.  I have found this tool to be a great help in figuring that out.  Even if my exact color is not matched on a card, there are enough swatches that I can at least determine which page it belongs on.  Here's to happy quilting!