I dont want to say that most boat owners are unimaginative and conformists...hey,at least they own and like boats.
But one major human characteristic is herd instinct. So because the "Boat Magazines" show mostly white and dark blue boats & Yachts, that's what you see mostly.
It is a bit like you only very seldom see a white or black Ferrari - they look fantastic in these colours, but the owners are afraid of being unconform (strange enough with Luxury goods)
There are some changes in Boats like the Pershing which comes in Black though.
But the nice colorful old boating days are gone as it seems...look at the old wooden fishing trawlers, painted colorful, being a real pleasure and variety for the eye. Same boring thing with sail colors nowadays.
So, by adding color to your boat, you can easily and cheaply show some personality and taste, sticking out of the boring blue & white boating world.
Regarding "Maintenance durability" of colorful colors...what a ridiculous urban legend...as if manufacturers havent learned by now to make them durable ;O)