I was just working with a bride on matching her bridesmaid dress color to the fabric colors for sashes and arbor fabric...we could not make a perfect match. I suggested that we go with a completely different blue to compliment the blue dress, instead of it looking like it's mismatched.
If you have a tough color to match - just use that color as your accent color - buy things that you find in that color - and use an easier color, that goes with your original choice, as your dominant color. It will make the colors flow, instead of looking like an error, and make your life much easier !
Tough to match colors that are popular down here on the beach are coral, turquoise, and tiffany blue. Be sure you have swatches with you at all times!