How closely does replacement carpet have to match the old?

Hi, I live in New Mexico and we got some water damage on our carpeting that is insured. The carpet was continuous throughout the house (looked that way anyway; of course there are seams) but only part was damaged. My question is how closely is the new carpet required to match? Dyes change over time so that a new match to an old color will not necessarily match after a year or so and beyond, and I don't want there to be a noticeable change in color. I don't want them to replace the whole carpet throughout the house, but can they just leave a seam in or between rooms, or in a doorway, or what? Thanks!