Although all colors are clear coated, regular black is more temperamental and takes a lot more maintenance in order to keep intact, over the years. On the other hand, a clean black car looks unbelievable (of course, color appeal is very subjective).
Ember Black is very complex and extremely rich. As a metallic color, it will hide easier any chips, scratches, etc. Saville Grey is the same. A, relatively, new color in the Volvo line up (like Ember Black) and has tremendous depth.
If you are looking at this, strictly, from a maintenance standpoint, I would rank them as follows:
1. Ember Black
2. Saville Grey
3. Black