Colors vary in the way they are presented, and in the way you view them as each monitor can be slightly different.
The best advice is to buy your coordinates from the same product line as the focus fabric, or to use the same manufacturers blender lines. Several of the manufacturers use a standard color palette that is also used in their blender lines.
When in doubt, call the shop -- most of them will be happy to send you small samples to help you select just the right one before you order larger amounts.