Well,
This is up to you but, even if warranty would apply, the logistics of it, i.e. either taking that speaker cover off and running it down to the boat dealer you purchased from, or, taking the time to hook the whole boat up and drag IT down to the dealer so they could "see" it in its place and THEN determine if it's a VALID claim, and then take however long it would take to either deny it or approve it. Then, if approved, how long would it be BEFORE they get to it to replace it since they'd more than likely NOT deal with color matching in the paint process and would just order one from the manufacturer, IF it's still available. If it's DENIED, then you're on your own anyways. It's incredibly doubtful the dealer would have one of those, specifically YOUR MAKE, MODEL, COLOR ETC. of that speaker cover IN STOCK at the dealership so, even if approved, they'd more than likely take quite a bit of time to get one.
See what I'm getting at? To me, the smart move would be to simply remove that speaker cover, then buzz it down to your local big box store like Lowes or Home Depot or even ACE hardware, then go to the spray paint section and hold that speaker cover up to the closest color matched cap of any of the available spray paint. Orrrrrrrr, simply take that cover off, and maybe the matching one on the other side, and simply PAINT both of them to the color of your choice. The whole planet is in love with BLACK these days so, you could do that and you'd have matched speaker covers and, you'd be done IN ONE DAY and absolutely ZERO hassle with any attempt at warranty.
I have done things like this many, many times simply because, in small-ish repairs or fixes, it's just soooooooo much easier to deal with the issue, and I'm done. Warranty to me, is for grand repairs etc. like upholstery that's coming unsewed, steering wheel falls off, motor quits or develops the infamous "check engine light", or any other number of things that are of too much cost and intensity for me to deal with and that's what it's for, to deal with the "big" stuff. Your choice here. Good luck.
Scott