Lots of good thoughts above.
I buy most of my quilt fabric online. Using the retailers' pictures and sometimes color matchers, I seem to do well enough about 9 times out of 10. The 10th time, I sometimes get a fabric that still works nicely even though not quite as expected, and I sometimes get a fabric to go in the stash LOL .
Thousandsofbolts has a color matcher, color finder, and a feature where you can see all the fabrics in a given line. On some of the other websites, I'll do a search for the name of the designer or collection name to help find coordinates. If I've got fabrics across lines but from the same manufacturer, it can also help to go to the manufacturer website and see what their pictures look like together.