Welcome to the forum,
Color matching of 11 year old fabric will be difficult / impossible.
Even if the identical color / fabric is identified and located, then the aged and sun faded fabric will still be different.
Also, there is variability from lot to lot of one fabric.
My suggestion is for the person doing the upholstery to bring a fabric sample book for selection. Also have the entire boat done with just ONE lot of fabric, not ordering additional material for one more cushion at a later date (that will never be an identical match).