The sand on the beach in front of the Four Seasons, Nevis is has a darkish or brownish tint to it, probably closer in color to what you saw on many of the Puerto Rico beaches. It does not come anywhere close to the pure white sand you found on Anguilla, Grand Caymen and Aruba or the light golden sand you probably found on St. John, St. Barth's, St. Thomas and Antigua. As for comparison to the sand in the Bahamas that's difficult since you don't specify which Bahamas island you visited but here again Nevis sand is going to be much darker. You'll find a lighter sand color on the Atlantic beaches but the water on those beaches tends to have more waves.

Due to a combination of the darker sand, deeper water and the fact that the island lacks a comprehensive off-shore reef system on the Caribbean side the surrounding water has a distinct steel blue appearance rather than the bright turquoise blue you experienced in the waters off of Anguilla and the USVI's. The water itself has the same clarity as you found off of the other Caribbean islands you've visited but you should know the depth of the water increases more rapidly off of most of Nevis' beaches (Oualie and Camp's beach are the exceptions) thus giving one an initial false impression the water is not as clear as it actually is.

Becca, I've been to some of the beaches you list, and enjoyed the beach at Nevis FS as much as any of them. Sunnyboy's comments are exactly right - the water was very clear except when heavy rains stirred it up one day. It's not quite as technicolor WOW as St. John, and the sand isn't the white of Anguilla, but the palm trees and vegetation give the beach a very tropical look. The water temp was great in July. And Nevis is just a lovely place in general.