Agreeing with the others about the various issues of monitors and software and other issues. I have vision issues and have also adjusted my gamma settings, hard to explain but my screen is blacker/more saturated but is less hard on my eyes.
Just think about what a difference sunlight or Ott lights and various artificial lights can do to a fabric and multiply that.
You are going to have the best results matching fabrics that come from the same line, not just brand like Moda (which will help), but lines within the brand. I like the feature on equilter that lets you pick a color and then search for matching colors but I wouldn't trust that either. Basically, if you have to get a dead on match, you are going to need to do that in person.