Re: Sail Cover Material
The Sunbrella color that you see most commonly is called Pacific Blue.
I used to have a C25, and made sail covers for it. I suggest you use the existing cover as a pattern for the new one, if you decide to make your own. It isn't difficult. Take the old cover apart by ripping out the stitches. From your description, it should come apart easily. Trace the outline of each piece on the new fabric. I used a piece of chalk. If you want to extend the length or modify it, it isn't difficult to freehand it a little. Instead of zippers, I used velcro to close the front edge, along the mast. I never had the velcro closure blow loose, although it did weaken it's grip when the fabric began to wear out. I also made grab rail covers for my present boat, held on with velcro, and they have been through a hurricane without coming loose.
One characteristic of Sunbrella is that it unravels along any cut edge. The pros cut it with a hot knife, to melt and seal the edge. I prevented the edges from unraveling by sewing along the edge with a zig-zag stitch. The better choice, though, would be to buy a good hot knife to do it properly.
Making a new mainsail cover is a good winter job. You can take off the mainsail for the winter and bag it, and then take the cover home to make the new one in your spare time, without having to bother with covering the mainsail while it's on the boom.