I have normally not been a fan of white phones, or colored phones in general. So, I went with the Black Sapphire. I THOUGHT it was going to be a pretty true black, but much to my surprise it's a REALLY cool dark grayish-blue ... and as mentioned, depending on the intensity of light hitting the phone, and the angle, it really does seem to change colors at times to a silvery-blue. It's a cool color for sure.
Now, on the other hand, my wife got the white S6. She wanted the Plat-Gold, but they didn't have a 64gb version in the store, so she got the white instead and is just as happy. This phone - with the brushed metal bezel, and the pearl-white glass on the front and back - is truly a very elegant, pretty phone. I didn't think I'd like it, but I do. I would still choose my black sapphire for me, but I can't argue against the beauty of the white.
Funny thing though ... wife HAD an S4 active in black, but it got damaged and she had to get a refurb replacement. They sent her that teal blue-ish green one, and honestly it was/is hideous. The only redeeming factor of it was that it was easy to spot, and she knew it was hers because nobody else had that phone. So, for her ... going from that monstrosity of a phone (aesthetically) to the pearl-white S6 ... she couldn't be happier, all the way around.
Even funnier though ... her FAVORITE thing is NOT having that charging port cover anymore, and not always getting that message to make sure it's closed, and that other message always telling her to make sure the back cover is secured well for waterproofing.