A few thoughts:
1. I see you have a Florida zip code listed in your profile. For my tastes, Dark Blue might look good, but would be a heat-sink in summer. Could easily be uncomfortable to be beneath. A lighter color would be my choice. However.....
2. Complimentary color to Blue is in the yellow/orange spectrum. You could go off-white or champagne colored.
3. Also have to decide if you seek protection from sun, rain, or both. In general, three choices - Stamoid/vinyl is and will remain waterproof. Acrylic (Sunbrella) begins life fairl waterproof but it wears-out over time (albeit a long time). Textaline/Pfifertex mesh - used as the fabric in sling-chair outdoor furniture - gives filtered sun shade and only modest rain protection. Acrylic/Sunbrella is a good happy-medium for most.
4. Acrylic/Sunbrella comes in different grades - and not all colors are available in all grades. You are looking for 9-ounce fabric (Awning) vs 6-ounce.
5. Stitching demises long before the fabric. There are lifetime threads for stitching, but they are damn expensive ($75 for a small cone). But it will prevent having to re-stitch the top in 5-7 years (guesstimate for Florida).
Personally, I would stick with white or off-white; or maybe even Cadet Grey (
HERE) as Comodave suggests (it's a very light grey), or perhaps Silver (
HERE). Cadet Grey has some taupe-like hues that may not coordinate well with your hull - definitely get samples of each, and order a yard of your final choice before committing. I would not go with solid vinyl such as Stamoid because in my experience, it can mold a bit on the underside. It is very long lived and of course very waterproof. That said, Sunbrella has a relatively new fabric "SeaMark"(
Cadet Grey HERE) where they bond a PVC layer on the underside of their acrylic fabric to make it waterproof - this might be the perfect combination of Sunbrella fabric appearance yet long-term waterproofness. Or it could delaminate in 5-years. I don't know, but it looks intriguing to me.
Good luck - plenty of pictures please.....
Peter