Interesting that you should ask. A friend and I are working with a certain focus fabric and wanted fabrics to go well with it. I am also working with another focus fabric on different projects but they have the same general colors for the most part. I recently put in a big order for both of us, got it, and it is exactly what I needed. There were 45 different fabrics in that order. They are all perfect. Here's how I did it:
I took pictures of the focus fabrics (you can get these from websites or your camera) and put big copies of them in Word. I checked them against the fabric itself and was sure the colors were exactly as shown and read correctly on the monitor I was using. I was able to check one focus fabric on the site, as it was for sale then, and it was accurate. I then used their design board against my Word file like with a split screen.
The site is equilter.com. Paul Rubin, one of the owners, built his own design wall feature. It is VERY accurate. I have done a number of orders with them using that design board and have never been disappointed. You can easily use 85 or more swatches, and move them around. Their scanning process is accurate and true to color. What you see is what you get. They also give excellent descriptions of every color in the fabric. So when you see a swatch on the design board and on the site, you can be sure it is accurate. Just be sure your monitor is: I have two monitors and only one is really accurate.
Their prices are no higher than anywhere else and their service is great. They are my first stop when I'm shopping for fabric online. I've never been disappointed in all the years I've shopped there.
By the way, I am almost always disappointed at fabric.com. For instance, one fabric I ordered was supposed to be purple and it is really grey. I have studied colors for many years and taken many classes in color theory; I am very fussy about colors and pay close attention. I haven't been happy at all with fabric.com for the past several years. If I buy fabric there, it is on speculation only. In other words, it may have to go into the stash if it isn't as I thought. When I buy at e-quilter, I use every fabric and get great results.
My quilts are known for their dramatic color combinations. I get a lot of compliments.