Not only does this allow you to match solids of the fabrics you already have in the house, but it provides the exact name and number of that color so that you don't have guess when you go to buy it! The biggest dilemma people face buying solids online is not knowing how true the picture is to the actual color of the fabric. This is true for all fabric, but it presents the most problem with solids.
Here is the exciting part. Fat Quarter Shop has kindly offered to sponsor the giveaway of two Kona color cards and two Bella color cards! I will pick winners on Friday (since I will be working in the field all week...boo) and all you have to do is comment about solids to enter! I use my color cards religiously and they are truly a great tool to have in your sewing arsenel. You can also find them on Fat Quarter Shop here and here.
Kona solids are the trusted, turn to line of solids that everyone knows and loves. They have quite an expansive range of colors (over 230!) and are carried by most fabric stores. I have recently, however, fallen in love with the Bella solids. The are more of a newcomer in the last couple of years, but they have some fantastic colors. They are winning right now as my favorites. Oddly enough, very few colors repeat between these two lines. If you have both color cards, there is almost no color that is lacking. I have both tacked to my wall (because I think they are beautiful, haha) and I consult them on a daily basis.
I hope this helps if you have been struggling to find the perfect solid online! I know that the fabric stores near me don't carry very many solids, so I have had to start buying mine online as well. If you buy solids online regularly, a color card is a must have!